I love the sound of a great guitar through a vintage style tube amp. This probably makes me somewhat of a looping oddity...I like the contrast between old school sounds & new school techniques. Thing is, that forces me to run the EDP in front of the amp. Some guitar/amp combos fare better than others, but it's certainly a compromise. Sometimes it's not even that -- it just sucks; lots of noise, decapitated high end, etc.
So, I take it that the solution is an effects loop. But it's a pretty rare '62 Princeton that has an effects loop, and I'm not about to mod mine so extensively.
If I understand these things correctly, adding a mixer won't be any advantage (although it'd let me use other instruments, but let's stick with guitar right now.)