It will have u install cios251 (d2x base 38), but these is only needed for spongebob boating bash and usb keyboard support in animal crossing. Also ModMii can help u update apps if u haven't done so manually since using modmii last.
With the cheat code downloader fixed u can grab a complete backup of what was on geckocodes
I'm curious, you should use modmii's syscheck analyzer, it will probably just recommend cios251, depending on how long it's been since u used modmii last
Oh and u can use modmii to help u set up a dual boot neek setup
What else... If u use riiconnect24 modmii's system menu IOS may be helpful, but not necessary unless u need both functions of rc24 and a patched system menu ios, then u can just keep your current system menu IOS if u don't have issues
U can do almost a full softmod on a wii without an SD card with modmii's guided support
Etc.
Edit: u could also install modmii's updated usb loader forwarder channel for reordered paths/priorities and faster load times