IMHO as it's reached £7.1K so far it's really close (perhaps even past) it's 'money' if it hasn't been run so far and the seller won't start it. Being as none of us are interested enough to phone the seller and ask leading questions we won't know will we?
I'm minded to recall a ZR1 I could have bought about 5 or 6 years ago. It was higher mileage than this one, very presentable inside and out and up and running. It did have an irregularly running engine issue which the owner couldn't seem to get resolved....don't think it was a mechanical problem, seemed more like an electronic, vacuum or sensor issue. £10k would have bought it. He didn't want any come-backs from unhappy buyers and chose to let a trader take it.
C4's of any description are simply not on most UK buyers hit lists as future classics, 99% of people wouldn't have a clue about a ZR1 anyway. Canny buyers can hopefully pick up a good stock C4 for comparatively low money (much as they would a C3) hoping its value will hike-up in future years..........just don't hold your breath too long!