Well I'm now in a position to answer my own questions.
I couldn't resist the bargain, and now have (temporaily at least) both a VW11 and an HS20.
Firstly, what swung me to purchase was that the HS20 uses the same ceiling bracket as the VW11, the PSS610.
So I could just swap them over.
Secondly, the throw distance seems to be the same, so I don't know what all the talk of the HS20 having a long throw is all about!
Anyway, the HS20 is slightly quieter than VW11. Its not night and day but any reduction is good. The tone of the fans is very similar.
The contrast is quite a bit better. This was the main reason for wanting to upgrade and I'm glad I did. For £1500 notes this is value for money!
There's more snap, effortless contrast, more vibrant colours (particularly red, which is good thing) and with the iris shut, black levels are better too. Some shadow detail that is invisible on the VW11 becomes visible on the HS20.
Its actually made me wonder if my VW11 bias settings are up the wall... but I've never fiddled with them they can't be.
This is all comparing to the VW11 with its CC40R filter attached!
Micro lense array helps a tad, but not worth shouting about.
The only thing that I would have hoped would be an improvement is with video noise. There are some very dark scenes where a bit of noise creeps into the picture on the HS20. The VW11 is totally noise free, and in this regard it still has the edge with bright animated films like Monsters Inc.
But I wanted a PJ that delivered more snap with regular movies, and the the HS20 delivers.
Its early days I know, but I'm pretty chuffed and will be flogging my VW11 soon.
Overall, IMO the HS20 is a worthwhile upgrade from the VW11 at £1500 until 3 chip DLP's come down to sensible prices.