Whoa, really? they're......common? How much are the Gamecube Hori Digital Controllers? I've never ever seen one instore, or indeed the US model. I have seen the Pelican one before, but not in years.
Not that I don't believe you, but it takes a lot to wear out an snes pad. I have Atari 2600 joysticks from the very early 80's that aren't worn out, and all my NES controllers still work like a charm 20+ years later.
As you stated, if it is real bad, simply get another one, but if you shop on ebay make sure you pay close attention to the picture and read the description. The Super Famicom itself is quickly approaching its patent expiry and as such ebay is already flooded with Super Famiclone controllers. Unlike the Nintendo ones, these will wear out as they are made of much cheaper materials.
Lastly, regarding Soul Cali 2 GC, I'm pretty sure it allows you to remap the controls as do most fighting games.
The main reason I like my retrozone SNES to GC adapter is to play Ikaruga, Megaman Network Transmission, Megaman X Collection, Sonic Mega Collection, Sonic Gems Collection, Soul Calibur 2, Resident Evil 1-3, and the classic Zelda titles.