The only reason I've never really felt like picking up Super Circuit is because I never cared too much for the controls of the SNES version, and I assume they're fairly similar. That being said, the courses look really well-designed (though I'd say they're every bit as "weird" as 64's, which isn't really a bad thing at all in either case), and having never heard of the red shell trap, that sounds really sweet.
Mario Kart 7 could really stand to have one cup for each of the previous installments of the series, but my guess is that it may forgo SNES and GBA entirely. I'm upset that neither Vanilla Lake from the former ever made it into a retro cup, but I did love most of the courses that were brought back, especially in MKDS.