Is it worth it? What's the major differences between Edit, Pro, and Suite? Will it load my old Movie Studio projects?

Hit me with your thoughts please.

No differences for Vegas itself between Edit, Pro and Suite versions. Only third party add on differs. All your VMS projects can be opened and further edited.

....and with the release of Vegas Pro 19 "soon", there is a sale.

As @3POINT, the only difference between the Vegas products are the "bling" (addons) you get with it. They all edit and have the same editing features outside of the addons. Many are quite happy with the Edit version.

Here's basically what's offered . . .

Vegas Edit 18 = Vegas Pro NLE + free upgrade to 19.
Vegas Pro 18 Suite = Vegas Pro NLE + free upgrade to 19 + Sound Forge audio editor, version 14.
Vegas Post Suite = All of the above plus the standalone, "Vegas Effects," an Adobe After Effects-like 2D/3D compositing and effects application. Also includes a bunch of commercial plug-ins from BorisFX' Continuum-series, NewBlue, and others—actually a very nice selection of premium effects.

Currently bundled effects add-ons with Edit/Pro include NewBlue Elements 3 Overlay, an excellent DVE-effects plug-in (also available directly from NewBlue Post for a promotional price of $49). BorisFX' Particles Illusion standalone is also included, but is available for free from BorisFX anyway so doesn't really bring any added value.

Alternatively, get Vegas Edit (or Vegas Suite if you also want the audio editor), and buy HitFilm Pro separately from FXhome, which is mostly the same product as Vegas Effects (though, branded differently), but also includes a few key pro-level features which Vegas Effects lack.

Personally, I would choose the Vegas Edit + HitFilm Pro approach since I already own a Sound Forge license bundled with a prior purchase of the now-discontinued Vegas Movie Studio 17 (not to be confused with the entirely different, less-capable, nearly identically branded Magix' "Movie Studio").

However, I won't get the pile of included third-party effects which Post includes, so I plan on buying the full-version of HitFIlm during their next sale, mostly because I'm interested in the plug-ins included in its sister-product, FXhome's Ignite Pro (which is sold bundled with HitFilm during their promotional sales).

Here's basically what's offered . . .

Vegas Edit 18 = Vegas Pro NLE + free upgrade to 19.
Vegas Pro 18 Suite = Vegas Pro NLE + free upgrade to 19 + Sound Forge audio editor, version 14.
Vegas Post Suite = All of the above plus the standalone, "Vegas Effects," an Adobe After Effects-like 2D/3D compositing and effects application. Also includes a bunch of commercial plug-ins from BorisFX' Continuum-series, NewBlue, and others—actually a very nice selection of premium effects.

Currently bundled effects add-ons with Edit/Pro include NewBlue Elements 3 Overlay, an excellent DVE-effects plug-in (also available directly from NewBlue Post for a promotional price of $49). BorisFX' Particles Illusion standalone is also included, but is available for free from BorisFX anyway so doesn't really bring any added value.

Alternatively, get Vegas Edit (or Vegas Suite if you also want the audio editor), and buy HitFilm Pro separately from FXhome, which is mostly the same product as Vegas Effects (though, branded differently), but also includes a few key pro-level features which Vegas Effects lack.

Personally, I would choose the Vegas Edit + HitFilm Pro approach since I already own a Sound Forge license bundled with a prior purchase of the now-discontinued Vegas Movie Studio 17 (not to be confused with the entirely different, less-capable, nearly identically branded Magix' "Movie Studio").

However, I won't get the pile of included third-party effects which Post includes, so I plan on buying the full-version of HitFIlm during their next sale, mostly because I'm interested in the plug-ins included in its sister-product, FXhome's Ignite Pro (which is sold bundled with HitFilm during their promotional sales).

Don't confuse Vegas Pro Suite with Vegas Post Suite.

There are no third party fx bundled with Vegas Post Suite unless it's a part of the special offer. It's Vegas Pro, Vegas Effects, Vegas Image and Soundforge.

With Vegas Pro Suite you do get the some Boris FX units, NewBlue...

You still have some time to inspect the VEGAS Pro / POST 18 product pages at https://www.vegascreativesoftware.com/us/ (or your area's version of that URL) before v.19 comes out.

Here's basically what's offered . . .

Vegas Edit 18 = Vegas Pro NLE + free upgrade to 19.
Vegas Pro 18 Suite = Vegas Pro NLE + free upgrade to 19 + Sound Forge audio editor, version 14.
Vegas Post Suite = All of the above plus the standalone, "Vegas Effects," an Adobe After Effects-like 2D/3D compositing and effects application. Also includes a bunch of commercial plug-ins from BorisFX' Continuum-series, NewBlue, and others—actually a very nice selection of premium effects.

Currently bundled effects add-ons with Edit/Pro include NewBlue Elements 3 Overlay, an excellent DVE-effects plug-in (also available directly from NewBlue Post for a promotional price of $49). BorisFX' Particles Illusion standalone is also included, but is available for free from BorisFX anyway so doesn't really bring any added value.

Alternatively, get Vegas Edit (or Vegas Suite if you also want the audio editor), and buy HitFilm Pro separately from FXhome, which is mostly the same product as Vegas Effects (though, branded differently), but also includes a few key pro-level features which Vegas Effects lack.

Personally, I would choose the Vegas Edit + HitFilm Pro approach since I already own a Sound Forge license bundled with a prior purchase of the now-discontinued Vegas Movie Studio 17 (not to be confused with the entirely different, less-capable, nearly identically branded Magix' "Movie Studio").

However, I won't get the pile of included third-party effects which Post includes, so I plan on buying the full-version of HitFIlm during their next sale, mostly because I'm interested in the plug-ins included in its sister-product, FXhome's Ignite Pro (which is sold bundled with HitFilm during their promotional sales).

Don't confuse Vegas Pro Suite with Vegas Post Suite.

There are no third party fx bundled with Vegas Post Suite unless it's a part of the special offer. It's Vegas Pro, Vegas Effects, Vegas Image and Soundforge.

With Vegas Pro Suite you do get the some Boris FX units, NewBlue...

Oh damn! Did I screw that up? I thought I got everything about right. Oh well, thanks for pointing that out.

To answer the OP, I definitely think the upgrade is worth it, if only for the Photoshop-like layer/compositing feature for video tracks (necessary to apply certain third-party effects, like clip effects-libraries). I just haven't made the jump because I've been waiting for Magix to rotate the bundled effects. They've gone past three or four "deadlines" without changing the free plug-ins offered (which they used to do quite frequently).

As I said above, only NewBlue Elements 3 Overlay is currently bundled, which I already have, and unlike FXhome, works on more than one computer (so I don't need the second license anyway). But unfortunately, the FXhome bundled plug-ins are limited to a single-install and is mainly why I'm popping for the full-version of Ignite Pro when the next sale comes around.