I play HDR/Super Turbo a bit for fun, too. Lyte might disagree, but while the match-up knowledge and quirks of that game aren't gonna help elsewhere, I find it to be a good back-to-basics tool for focusing on footsies and execution (excluding Remixed mode). Inputs are relatively strict and carryovers that are overly simple in SF4 - like reversals, for instance - require precise timing in ST. It's useful for when you've been playing SSF4 for awhile and suddenly find yourself accustom to inputting sloppy DPs as forward, down, backdown, back, forward + PUNCH and expect it to still work.
And it's fun and easier to temp your non-fighting game fan friends into playing under the pretense that they might actually win. (They won't.)