Ugh. I would hate that so much that i'd probably give up using Vegas in frustration. But, that aside . . .
You could keep a Windows explorer window open to that directory and then drag the file from there into the project media window. It's not automatic, but it would save you a ton of time over doing it within Vegas.
. .and the bizarre thing is that when I create a "still" - additional media that did NOT exist before, THAT is automatically added to the Project Media Window - think about that then! And it is NOT added to the timeline. A rendered timeline selection is newly created media? Why not add that to the Project Media? Also, applying non-realtime Audio FX will add this new WAV take within the Project Media.
So here are 2 instances of where NEW media IS being produced and added to the Project Media window. I think it is completely logical for a User, making Renders, to want, wish and desire for the same to happen to newly rendered Video. Yeah, Nick, I can see that and can see that as being both logical and possibly advantages. Now, how and where would you find this a boon to your workflow?
I would only accept this feature if it could be turned off. In fact, i'd even prefer the two examples that Grazie gives to be turned off too. Heck, i wanna just get rid of the project media pool completely! ;) But then, i've ranted that before.
Actually I would just like one more check box at the bottom of the "Render As" window that says "Add to Project Media". Simple.
OK, I've edited a project out of "raw" footage. Now I'm "archiving" the bits left on the timeline by smart rendering them to my archive drive under species name etc.. Then I want to bring them back in to the project in the same places but on a lower track and dump the huge "raw" footage files. So effectively I'm recreating the project with trimmed media that I want to keep permanently rather than messy large raw media.
How about "save project with trimmed media" and "render to a new track"? Either of these options will accomplish both trimming the media and placing it back in your existing project.