FWIW, and assuming that the driving part is something that people actively want to participate in, then in terms of fun roads I would rate Scotland above Wales. The IoM would also be above Wales if there were more roads, as what they have is stunning with no limit.
Something like LM is more of a static experience, as the drive down there and back is actually pretty dull. That said, the experience of the race itself is utterly immense and I WILL be back next year to do it all over again.