Do I Even Need My Mixer Anymore?

I geinerally find that a good mixer has better inputs than those little deals, no matter how good they are(often times you're going right into the A/D on cheap ones...).
If those things are all you're ever going to use, then I'd just leave them plugged in.
It also allows you to run them all at once if you want, and it'll let you just leave them plugged together with MIDI.
Syncing and the like...