Tough one this, I paid £700 (or so, can't remember exactly) for my '89 no MOT K model on ebay. About a grand later (full service, tyres, chain n sprockets, fork & shock rebiulds, wheels blasted & painted and a few minor bits n bobs and I've got a reasonable nick slingshot. I would describe mine as in good condition rather than immaculate with a few battle scars on the original paintwork and one or two fairing cracks. Wouldn't take much (paint job, bit of polishing and a new screen) to bring it up to very decent standard.
These bikes are right at the start of the 'appreciation curve', never going to be Vincent Black Shadows but given the ridiculous prices people are paying for LC's (great bikes, I've owned four but £5k for a minter, really?) who knows the limits. Right now I wouldn't part with mine for less than £5k but that's more about the value I put on it as a piece of personal (blue & white) gixer history. If someone offered me a slightly scuffed, but all the rights bits sorted, 1990 EXUP for anything over £1500 I would laugh so much they would probably clock me one, just 'cos not my bag, in a rambling sort of way just trying to say ............. at the moment a gixer '11 slingshot worth wot someone will offer you for it, don't be offended if it's not much