I have not seen the image from the Pro8100 in person. But it's over 2 years old and based on the review, the dynamic iris is worthless and annoying. So you would have to compare it's results without the auto iris. Even at $920+tax, I doubt it would look significantly better than the HD20 or HD180. If it even looks better at all. So if you already own the HD180, it seems like a waste of time to swap out for the Pro8100. Again, based purely on 2008 and 2010 updated reviews of the Pro8100.
And the size, is HUGE. The Pro8100 is almost 2 feet (FEET!) wide, over a foot deep (15+") and over 6" tall, at almost 20 Lbs! It's MASSIVE.
And as for LCD, it it's black level was put with the Panasonic AE2000, 2 models behind the current AE4000. Sure the 4000 has better blacks than the HD20. But not $1k more worth of black. So the Pro8100 is likely very similar to the HD180 and HD20.
So unless you really need the motorized lens shift and a massive sized projector. I think the HD20/HD180 is the way to go.