Ok, so if I don't plan on using the 26650 battery, then there's no point in picking up the mega over the original for any other reason, even the slight little improvements here and there? I know it has an improved screen and the firing button looks a bit larger (not that this is really a concern for me), but I don't really see any other reason to get it. I agree that they could have done more to improve on the original Pico if they wanted to release a 'new and improved' model of it, 5 extra watts in exchange for a bigger battery doesn't seem like a particularly great trade off to me.
I'm with @sawlight, I would (and did) go for the original. The screen is perfectly readable and the fire button is good, too. Almost anything can be upgraded, but that doesn't mean it needs to be. "If it ain't broke don't fix it" etc. etc.
Saw is there a new "istick mini" out/coming out or do you mean the really super mini 10 or 20W minis that have been out for a while?