I was in the same camp as you regarding rear fill, but Steve talked me into it and I'm glad he did! It has to be integrated properly so it doesn't pull the stage towards the rear, but when it is, it actually widens the front stage as odd as it sounds.
That's the problem with it. Crossed over low enough it shouldn't be an issue, but the higher in frequency you go, the more multi-speaker-path phase interactions there are - mix that in with the reflections that you already can't avoid from all your glass, plastic - stir that up with your inherently offset seating position - it's a phasing nightmare.
I generally like the concert approach. Not that I don't have exceptions - but I'd advise customers who were self-avowed SQ people, to invest in one good component set up front, rather than split the budget. I'm actually personally also a fan of a lot of electronic stuff that's weird and ethereal, or just has a club beat to it - and I think in all cases, it would be ideal to be able to replicate each of those absolutely wildly different environments - but I'm enough of an imaging audiophile nutcase and geek to acknowledge that's unrealistic without lots of complexity that can be so counterproductive.
I once had a '95 Pathfinder around '99 or '00 (back when they were more mini-truck than minivan substitute) that I did a bit of an experiment with a line array - an intentionally near-field line array. I used the neutral center spot between the headrests rather than my listening headrest specifically because I'm also anal about symmetry - but I literally tied a pencil to a string and drew curved lines down the new doorpanels I was fabricating. I mounted two 5.25" midbass drivers down in the corners, and four 2" full range drivers (I swear they were TangBand from PartsExpress).
The net effect was actually awesome. Eventually I added a super-tweeter in my sail panels that picked up way at 10kHz, just the final octave where the little 2" with their phase plugs rolled off around 12kHz.
But what was most remarkable was both the height and width of the stage - neither of which I'd predicted. I was actually trying to create more direct-to-center primary pathlengths, to dominate the reflected pathlengths. And what I didn't realize that I also did was simulate the way a single version of that 2" speaker would project sound towards you if it were several feet to either side of that actual location. For a cheap system, it was one of the best imaging that I've ever had - especially once I filled in those final 'ting tings' that were a little under-represented initially, with the supertweeters.
Four midbasses in that install - but for all intents and purposes, from the same location - not two front, two rear.
I'm curious when you say "intergrated properly", are you referring to phase alignment (timing), or frequency (crossover)?
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