The GBA is much more powerful than the SNES, which further hammers down the point on what a terrible port that is. And should also stress the fact that you should not use ports to judge the inherent capabilities of hardware. You're throwing the human factor out of the window which accounts for so much of the quality. Would you say the 360 is many times more powerful than the PS3 because the Skyrim port performed like crap on the latter?
I think a competent SNES port of Sonic 1 might be feasible. I'm not a programmer of course, much less an ancient assembly one, but it's the gut feeling I get from seeing similar fast paced on the system like Sparkster. There would likely be some notable concessions like more slowdown or flicker than usual when there's lots of objects like rings on the screen at once. It's all about redesigning select parts to better accomodate for what the SNES can't do as good, or could possibly do better in other cases.
"Blast Processing" in itself didn't really mean anything, but I think the benefits of the faster CPU cannot be understated because it gave programmers and designers so much more flexibility to do what they wanted on the machine. From all the interviews I've read from retro developers it seemed they generally favored working on the Genesis. For example Shiny utilized the CPU for an art compression system which allowed for more character animation frames on the Genesis versions of their multiplatform games.
