I have and use SpiceMaster and SpiceFilters 2. They're out-of-the-box good, providing you a lot of the looks that you might need or want from Vegas. However, there's also plenty of room to grow above the somewhat "cheesieness" of the stock effects -- they're plenty flexible.
If you need a software stabilizer, I suggest Dynapel's SteadyHand -- $69.
I love Pixelan for the softness of their spices and
the power to create new effects.
Great add-on to have.
They have demo. Download and play with it.
Mike Fereer provides great supports.
Others good effects plug-in like
www.borisfx.com
www.prodad.de
I have just received the adorage vol 7 which now supports Vegas as a plugin.
I have only just installed it and will not get around to looking at it in anger for a couple of weeks. It did arrive with an additional CD called Dynamic wipes which at first appearance provides some of the SpiceMaster 2 capability
The Adorage 7 stuff looks interesting but some of it is a bit cheesy. Some good stuff for event work like weddings, special events etc.
Maybe worth a look depending on what you want to do.
It all depends on your needs. It's a good program and produces nice transitions. I paid $200 for it and $300 on Ebay for a new copy of AE 5.5 Productions bundle. For dramtic visuals look elsewhere for some nice editing effects it will work.