I've been in airsoft since the late 90s.
A couple of years ago I switched to GBBR. I'm now selling off just about all of my AEGs.
If you play milsim and/or real cap and/or want a more realistic experience, GBBRs are way more fun. Where I am sticking to AEGs (for now) is support guns; if you skirmish a lot, if you enjoy unload highcap/midcap after highcap/midcap in full auto, GBBR is not the way to go.
Money pit? No more so than most AEGs. In all these years I have yet to see any "silver bullet" gun that was perfect out of the box (many TM pistols and shotguns come close, but the plastic bodies are a shortcoming in my book).
More maintenance? Yes, a lot more (not unlike a real gun; clean it after every use) but maintenance is not unlike a real gun's and nowhere near the headache of taking apart an AEG/mechbox. I can totally clean my GBBR in about 15 minutes start to finish.
I run all WE GBBRs. Initial "upgrades" are minimal: NPAS is a must, but cheap. I also like a heavier buffer. Anything else can wait. Don't partial upgrade internals with steel RA-Tech parts "in case" something breaks; from what I've seen, the steel parts will destroy the stock ones and cause other problems. So if you go RA-Tech you gotta do the whole thing (bolt carrier assy, trigger pack, valve knocker). Mine are stock and are fine, I don't feel there's a need to replace them and honestly given the price I think it's more cost effective replacing anything that eventually breaks with an OEM part.
Mags are more expensive and troublesome (even by gas mag standards). Not the end of the world, change some o-rings once in a while, maybe have to do a re-seal. But it happens, its annoying and you have to take care of it. Price-wise, keep in mind at $40 a pop, if you're planning on loading out 10 mags that's an extra $400 right out the gate, definitely something to think about.