Yeah it's a bit of a balancing act with scale, and realistic scale isn't what I want of course, but I was rather shocked when I swapped in some realistic stuff and I started to feel like the game looked... kinda dumb.
Yeah that sweet spot of good vehicles with clean silhouettes and a low polygon count is hard to hit on the asset store. Any objects with "cartoon" on it is usually on the minecraft side, with a few exceptions like Toon Soldiers by Polygon Blacksmith (which is going for a TF2 look). I've seen Simple Apocalypse but never looked closely at their vehicles because they put all the lego-styled characters front-n-center. ...the vehicles aren't bad... I could mayyyyyybe rough them up a bit in texture to help them match my other stuff (mostly Battle Cars from Evozon and War Cars from Havolk). Actually the vehicles in Synty's Polygon Battle Royale pack might be better (although both would mean spending a fair amount for a small percentage of usable stuff).
I'll bookmark them and check into them once I use up my existing cars. Thanks for the steer!