I have never used receivers, even before AV. So I can't comment on improvement. However, I think reliability is the issue for me, as well as the design concept. I just think that cramming a bunch of power amps, preamps and processors, running off the same power supply and placing them in one case, is just poor design and bad engineering. Personally that is something I would not countenance. I would suspect though that in a high end system, there is likely to be improvement is audio quality, especially when pushed hard. For reliable concert levels and full dynamic range, really does require more power than can be provided by a receiver.
My rig never gets close to running out of headroom, and has a relaxed sound under all conditions and program. Lastly I have an absolute need for xlr balanced connections.