distance from display 60"
option 1: status quo
40" LCD
bookshelf speakers
sub
option 2: new display, smaller/crappier speakers
54" plasma
not ideally placed bookshelves OR small (tiny) speakers
sub
I vote for 40" assuming you can find a good quality picture at that size.
Otherwise, perhaps a 42" plasma. I know Panasonic doesn't make their best model numbers at that size, unfortunately. I did a quick google on smaller/older Pioneers, none around, not surprised (they only seemed to make 50" on up at a certain point in time).
The size sort of depends on what you're watching. If you're like me, +99% bluray, I can see going up to 50, 54, but if there is any significant portion of SD viewing, or gaming, or even HDTV, I'd stay at 42" (which can still seem overwhelming in viewing angle, depending on the source material). That all said, 54" would be the closest to replicating my front row viewing angle (beats mine out by 0.8 degree). Again, no exaggeration, +99% bluray. I would not be surprised if I experimented with viewing angle more than any AHer in history.
At any of these sizes/angles, 1080p is a must, even at 40". Even at 37" it is an absolute must (still over 30deg angle). And even when smaller than that, will you be benefiting big time.