Interesting points so far. Just one thing for clarity: this is only for infantry combat. As soon as helis, arty, PBRs and tanks are in the frame, I am going to 6mm.
So my question then what rules are you using? If you;re using multiple figures on a base then 15mm is the way to go. Individually, I think that 28mm is very much prettier, as evidenced above, especially if you’re wanting a characterful game.
"I saw this in a cartoon once, but I'm pretty sure I can do it..."