I've had my R30 for close to five years now and bought it in just about perfect condition for very, very cheap and was offered a bit over double what i paid a few weeks after buying it... So they're are a very sort after car but only by people who know what they are...
i don't think i'd ever sell mine unless some offered me a rediculous price for it
and with a Ford GT Phase 3 selling for a tad over $500 000 down here in Melbourne at auction recently, rare or sort after cars can be a good investment in the long run....