I sometimes enjoy seeing game remakes. Most of them are crap (especially on the PC with Klik 'N Play!) but there are always a few gems to be found. And perhaps if your team works on a remake it'll be easier than designing something from scratch, so you'll build up some skills as a team and then be able to better create something totally new in the future.
As for Sonic the Hedgehog, that would be awesome on the Amiga, it could do it no problem. Heck, there's a Sonic demo
for the ZX Spectrum. Sega also seems to be very lenient regarding fan games since there are many Sonic games for the PC on the net and I've never heard of any trouble. The Sonic Fan Games HQ
has been running for years. But you could always make a Sonic-like game with a different looking character.
You know what I'd love to see on the Amiga? I decent Double Dragon remake! The official version was terrible, it didn't do the Amiga justice at all. Double Dragon 2 was better, but the first one has a special place in my heart since I enjoyed playing the arcade version.