That's interesting... some time ago I did the same with all my Dosbox .conf files. I noticed that when I used the Dosbox Log function it was warning me that there was a discrepancy with sound samples rate between my file (which was set at 22050) and SDL, which defaults at 32000. So after changing my mixer rate to 32000, I immediately noticed less audio stuttering in the games.I think i solved the small slowdown issue with the game Mario Kart: Super Circuit on the mGBA Wii.
I was using @SuperrSonic's RA-HEXAECO's (modified RetroArch Wii) core of mGBA Wii. I just set up the sound sample rate to 32000 Hz / 32 kHz (instead of 48000 Hz / 48 kHz) and then i saw for a few moments that the slowdown has disappeared in these moments. I didn't play it for further but i will test it more.
I could also used the Wiiflow-modified version of WiiMednafen 0.3-SNAPSHOT in the Wiiflow Plugins Pack by @Tetsuo Shima, here it runs at an acceptable framerate but it has a heavy frameskip and it also goes a bit slow sometimes. So I prefer using mGBA Wii.
Greetings
So now I'm wondering, is that possible that ALL wii homebrews should require a 32000 Hz sample rate?