I'm still weighing my options. The first project in my new garage will potentially be a little messy so I'm looking at maybe VCT for a year or two but I don't want to ruin my chances for a cool concrete floor later on (grind and polish, I think) - so do I need to seal it somehow before VCT adhesive (if I even go VCT..)? Will it help prevent staining for later on?
Typically speaking, you shouldn't apply VCT tile adhesive over a sealed concreate floor (paint or any other sealer). That said, though, 20 years ago I epoxy painted my garage floor and later, roughly 2 years later, laid a classic black & white Armstrong VCT tile floor. Over that time, I've had no issues with tiles popping. That said, though, I would NOT recommend installing a VCT tile floor as a temporary solution. Removing the tiles is a slow process (chip chip chip) with glue removal to follow. Then you would have to sand the floor smooth before applying anything new. NOT WORTH IT!
A few things about VCT tile:
1) Rubber tires will permanently stain the tile, with or without wax. This means that you will have to have something under each tire.
2) It's obviously softer than concreate and will gouge. If this is a working garage, not just serving as a space to detail your car, maintenance will be common. Replacing any severely damaged tile (or live with it).
3) A waxed floor can be VERY slick when wet.
4) I wouldn't plan on washing a car or anything that would result in prolonged water on the surface of the tile. Not really designed for that.
That's a few things to think about.
I installed my VCT tile 18 years ago and it has served me well. I keep my garage cool during the summer and warm during the winter, which I'm sure has helped. I went that route because I couldn't afford the better and more expensive interlocking options like we see today. I'm not completely disappointed with the choice, but I am currently replacing and refreshing the old tile floor. Chipping away stained white tiles and actually adding a third color to the mix.
Good luck!