My dad asked, "How much do you have into it?"
I told him, "$15,000."
He then asked, "How much could you sell it for?"
I told him, "About $12,500"
I took the wind out of his sails with that one, I knew where he was going. I'm building the car I have dreamed about, and honestly, what new car could I buy for $17,000 that is worth a damned? NONE, so to me it's no big deal to put the money into and acknowledge that some of it isn't going to be recovered. Now if I suddenly got in a bind, then yeah that would sting a little.
Also, even if you want to restore one, start with a good platform. A car without rust is existentially easier to restore than a rusted out one.