It would be nice to have more Sonic only area abilities, but the Sonic Heroes thing really was kinda lame, because I never really noticed that I could do it. Also it would be impossible to do it correctly with SRB2's thok.
I don't really agree that we need a clever way to make a Sonic only path, however. Personally, I've always thought we should implement Knuckles' lower jump, making it easy to split Sonic/Tails and Knuckles paths, like S3K did. All that's needed is an unclimbable wall and a jump of over 104, and Knuckles can't go through. Since the breakable walls are almost fully implemented as well, that would allow for Knuckles only paths to be created rather easily as well. If everyone remembers, there really weren't any Sonic-only paths in S3K. Instead, there were just areas Sonic and Tails couldn't reach, Sonic couldn't reach, and Knuckles couldn't reach. I don't see why we need to worry about making a Sonic only path when S3K never really had any. =P