Those look great, ads - I didn't notice that two of the bikes were paper until you metioned it! Card models are great fun to build and don't require any more care in handling than plastic models do. And, as your collection shows, the results are equally pleasing.
I'm surprised at the results you obtained with the craft paints. I use acrylics, too, but I've always used the expensive, brand-name stuff on the assumption that it must be better because it costs more.

But I've heard from a lot of people that get good results with the craft paints, and I think I'll give 'em a try.
BTW my daughter just bought herself a little Yahaha scooter for buzzing around San Francisco in, and it's all I can do to resist seeing what one of those rascals goes for these days.