I think in reality, it is easier (and more fun?) to be creative the more limitations you have. Of course, if there are too many limitations it also kills the creativity since you can't do anything. So, somewhere there is an optimal trade off for creativity and it may be around the C64 level. It is not too complicated to wrap your head around how everything works in it. If you dig deep though, not everything is as it seems which is where the real creativity kicks in.
The challenge is to 'beat the game', i.e. take the system beyond what it was meant to do. On an Amiga it is hard to utilize all its functions the way they were meant to, and on a PC it is almost impossible since it will do almost anything you can imagine (rendering things in ridiculous resolutions do not count).