I'm interested in using footage shot as 60i (or 50i) and 24p in the same project. I need the 'video look' and 'film look' in the same project, in different parts, specifically.

What do you think? Just drop the 24p in a 60i timeline and render-out as 60i?

Some 24p comes wrapped in a 60i wrapper, and it won't lose the "film" characteristic when edited as 60i. If this is 24p without pulldown added, you can render it in Vegas to 60i by adding pulldown, to get the same result.

Every year I do a show DVD for the animation students at the college I work for.
The final projects are a mix of 2D (720x480 from ToonBoom) at 24p and 3D (720x486 from Maya) at 29.97.
After doing a lot of experimenting to figure out the best way of doing this, I simply drop the 24p on a 29.97 project and let Vegas deal with it.
No complaints yet from the students and instructors and it's been 5 years now :-)
BTW, the teachers are blown away by the fact that, if they were to use Vegas, they wouldn't have to make a circle at 720 x 540 to get it to look like a circle when it's get shrunk down to 720x480/486 like they do when they use Premiere or AE.