I know how you feel! I feel the same way about my Avantime. The only other car I'd consider at the moment would be the Citroen C6 - Soooo comfy!
Same here Hugh, I just can't think of anything that would replace my Vel Satis for similar money.
I like C6s but they're about £10-12k second hand at the moment, much more than Vel Satises and Avantimes. I've thought about the Lexus GS300 (not the brand new one, the one til about 2004/5), the Jag S-Type or a Volvo S80, but they still don't offer the huge space that Avantimes and Vel Satises do, for the money.