You've already seen how useful room correction is for your set-up. More advanced correction will clean up the sound even more.
If you are happy with the volume of your system today, and you are not hearing mids and highs breaking up, then I'd say you don't need more power. You have about 20 dB of headroom in your system assuming a nominal listening level of 82 dB at 8 feet MLP.
Well that was my first experience with it, but the Onkyo room correct set the cross over of the M5s at 200hz to begin with and it did get the cross over right on the VP100 this last time i ran it at 80hz. I changed the crossover to 60hz on the M5s and noticed a marked improvement.
Volume wise I don't think I need more. I can see how people really get into the fear of missing out with audio equipment. There's so much choice out there and features its hard to say if things are worth it to you or not without actually buying it.
Frankly, I actually like the sound that comes from the vp100 so much it makes me wonder if I should have gotten the M22s instead of the M5s. Not that I don't love the M5s, as I do, but its just one of those what ifs with this stuff. I can see why "audiophiles" are always looking ot upgrade their setup based on crazy number of options and price brackets equipment comes at. To me the speakers will be a purchase I will use until they break or outlive me. But its like with this receiver, if I keep this one, will I be missing out on better sound if I get the xt32 correction?
Fun times with this stuff.
