New project! 1973 Volvo P1800es

Yes, it is desirable.   Yes, it is salable.   The problem is that the sellers always seem to have
an inflated idea of its value.   As a result, they sit for years with a For Sale sign, but are only
sold when the owner dies and his family just wants to get it out of the driveway.   That's what
happened to two that I've seen.   Unfortunately, in both cases, I didn't know that the guy had
died, so I missed out on it.

Don't put any money into it in the expectation that you can sell it for big dollars, because you
will never recover your investment.   Restore it only because you love it and want to drive a
classic.   On the other hand, it would be a shame to LeMonize such a beautiful car.

Personally, I would love to have one to restore and drive, but not at the prices that are being asked.

I sold a really rusty, rough one that ran for about 1100 on eBay a few years back. A fully restored, Barrett-Jackson-grade one might fetch between 25,000 and 30,000.  They'r somewhat rare, and becoming more desirable.  Rust is their worst enemy, because, like the Karmann Ghia, they dopn't have many bolt-on body panels, so you really need to be good at body work to fix a rusty one right.  On the other hand, the mechanicals are pretty simple, and the only somewhat trouble-prone component (the Bosche fuel injection) is easily replaced with a Weber or two SU carburetors. 

If you can coax it to life (shouldn't be too hard) and get it driving, provided there isn't any major rust hiding anywhere, you could probably get between 3 and 5000 for it. 

if you want to keep and drive it, make sure you can keep it garaged (the rust issue), but other than that, they're pretty reliable, fun-driving cars.  Not the fastest sprinters, with only about 125 HP on tap and ~2500 lbs, but the handling is very direct and the brakes are good even by modern standards.  They generally have overdrive, too (assuming its a manual transmission) so they can cruise on the highway.  They'll do 100 mph and the engine will just sing.

We are in the midst of a multiyear project to build a Lemons one, it started life with Evil John, and its on a rotisserie right now as we are protecting the bare metal of it from rusting away.  TBH its a back burner project as life has gotten in the way of completing it, but we will eventually.

Great cars, cool looks, performance parts are out there, they can corner and handle VERY well.  I'm excited to finish ours some day.