Wouldn't you know it. After all that time I spent thrashing Technics, I decide to give them another shot, and end up buying one.
So what did I miss on my first try? Well, it turns out the sound is quite impressive through a good pair of headphones. And I can live with that. It's something I should probably be doing more often anyway, since I'm in an apartment.
I finally ended up with the PX663. More expensive than the P50, and much harder on my rapidly aging back, but the P50 would only have the sustain pedal, and I've been using 'the other two pedals' a lot more lately.
The grand piano sample is lovely. Definitely Steinwayish enough for my taste. (Don't tell Steinway, I taped their logo to the front panel!) There's also an upright sound, but it has a VERY sudden break in tone in the low bass, which is rather unsettling. Also I would have liked a lot more reverb capacity so I could pretend I'm performing at Carnegie Hall.
The action will take some getting used to, as the keys make a fairly sizable 'bang' when they hit the bottom...I might have to invest in some closed DJ-style headphones. However, the touchweight is not as flimsy as I remember. While it's less crisp than my Roland, it's still reasonably solid, and the response curve actually feels a bit more piano-like.
I had one scare, one of the keys made a LOUD clicking sound. Seeing that the nearest service center was many miles away, I decided to take a warranty-voiding risk and pop open the case, hoping I could fix the problem. Fortunately I was able to diagnose it (one of the hammers was slightly misaligned), fixed it, and went back to playing merrily.
Overall I am pleased. It's a little nerve-wracking knowing that the manufacturer has dropped the line, but I'm just going to enjoy this while it lasts. Only problem is, my poor little apartment now looks like a piano store.