I'll give you my two pence worth having owned both.....
Firstly, its not Vauxhall, it a rebadged HSV, sort of like the Alpina equivalent for Holden.
Like you, I had the itch for a V8 and a mate owned a Monaro followed by a VXR8. A workmate was looking for a new car not long after I bought my 335d and VXR8's were being sold by dealers as pre-registered for £23-£25k to sell the remaining stock, so I pointed him in that direction. Every time we met up, I loved the noise and the way it handled for a big car, and his was bone stock.
Standard VXR8 is pretty quick, not as quite as quick as an e9x M3 though, but thats like comparing apples with oranges. The seats in the VXR8 and big, supportive and very comfortable. The interior materials arent as nice as a BMW but I didnt buy it for the interior
I've been on a few Pistonheads meets/runs and nothing short of exotica gets as many looks - probably because of the noise it makes and the fact that 95% of people havent got a clue what it is. I've never had so many random people come up to me to talk about my car, it certainly gets some attention, be that a good or a bad thing
Its basic, easy to service/replace parts and very easy to mod. Intake, Exhaust and remap will free up about 40-50hp, Supercharger will take you up to over 600 and wont cost anything like £12k
Gearbox isnt the best feel, parts can be expensive if you stay in the dealer network, its hard on brakes and suspension, it needs a fair few mods to really open it up (Exhaust is first on virtually every owners list as the standard one is far too quiet, standard clutch is pants but most have been replaced with LS7 under warranty), there arent many specialists about, ignorance/badge snobbery
Would I buy another? Thats a hard one... but nothing will make me part with mine short of buying a GT-R
Gratuitous pics of mine:
And a short clip of the noise