I'm currently using Tamiya acrylics through my airbrush and I was wondering a bit about glossing paints.

I know that Tamiya has a "matt" bottle that is essentially an additive that creates a flatter matt finish in paints when dry. I was wondering if there was a similar "gloss" additive. If not, can Future floor polishing be added to paint?

Or is it simply better to apply a coat of Tamiya acrylic, THEN a coat of Future? I just wanted to avoid too many coats of paint if possible.

I like your way of thinking Rich....I too think that the more coats of paint you apply the more detail you're covering.....I have never tried adding gloss to flat paint....but somehow I doubt it would work......I once heard that some paint company was going to come out with a line of military colours in gloss.....wouldn't that be great?!?!?
If you're brave enough.....give it a try....on something other than your model of course....and let us know how it works out for you.
Good luck

If you're airbrushing light coats, build up should not be a problem. If you ARE loosing detail from airbrushing, you are running too thick a paint mixture. from my experience, that is easy to do with acrylics, especially Tamiya. I've always thought it looked to heavy when it got on the model. I very rarely use acrylics, prefering enamels when I use the airbrush.
to the question at hand, I don't think you're going to get adequate gloss from a flat paint to safely put decals down, even by adding a glossing agent.

I'd step away from adding "glossing agents" or "matte agents" in the paint. I just use my tamiya colors as they are, and spray a matte coating over that when all is finished. To make it glossy, just spray a gloss coating over. Don't overdo this. several thin layers are better than one thick layer. A few thin layers of glossy coating can make your model shine like a mirror.