Thats why you use a two sized hit circle. One where the downsized approach circle hits, and one that indicates the hit box. With good coloring/shading/texture you can make it so that its not confusing at all.You still have the original circle (indicating the hit box) + another circle. I can't imagine how having a thick/double approach circle would not be even more cluttered. I think it's a feature worth considering. And going with what hadis1000 said, my accuracy changes dramatically on different scroll speeds in mania. Having this would allow players to find that sweet spot where the approach circle isn't too big to overlap a bunch of other approach circles, yet not so small that you don't know when to hit it.
Updated the first thread with the depiction of the idea.