I'm pretty sure Super Gameboy was supported in Masterboy. Maybe try Emumaster since it's based on Masterboy and see if it works. Could also be the rom.
Card speed cannot increase unless the bus speed increases which would require Nintendo making a Wii with a higher bus speed. It can't just increase by itself.
It's probably trying to read the dol off the other sd. That be my guess. Just have everything on one SD. Delete cover (or disk) art if you have to save space.
Go to 6.20 pro b-10 with permanent patch (like Rydian said). You actually get to play more unpatched games. PSN might actually work on 6.20 idk since I run 6.60ME 1.8.
I think gpSP has a bug sometimes with saves. It happened to my friend when he was about 95% done Golden Sun. You try the latest gpSP-J and get it into English here.