Rupert,
I've been down the same path...and apart from the Ali block, done every upgrade possible to my Vx. Inc a recent full re-build.
I thought about the swop to Duratec as I was having it re-panelled, but I decided to stay true to the vehicle's heritage. Also, in going over to duratec, there was the issue of changing all the anciliaries etc and my costs were already running close to 20K
I wasn't owning it to win races, and if a slightly better Duratec comes passed me at Spa....so what...weighing 517kg and with 265 horses under the bonnet that does not happen often anyway
I think the Vx has a certain charm and from what I've seen they seem to be a bit more popular now than say, 4/5 years ago when the developed K's were all the rage.
Good luck..