Interesting question and one I weighed up heavily when I bought mine in August.
I had a Mondeo st diesel, which did about 40mpg in the city. Desperately dull, never felt the urge to just get in it and just drive.
For an extra £30 a month tax, I can drive something that makes me smile every time I start it.
My fuel cost has doubled from about £80 a month to about £160.
As for resale, I've been watching the prices on this forum since about 2014, and I'd say they've stabilised. You could probably buy one and pretty much get your money back a year later.
I would say that the Lexus ISF is probably the most reliable V8 around. No rod bearing issues to deal with, no carbon build up to worry about, no head bolt issues.
About the worst thing you may have to deal with is a water pump leak, which would have probably been addressed if you're looking at an 08 plate.
V8s are a dying breed, I'd advise you to scratch the itch whilst they're still around and relatively affordable.