I don't see it that way. I've owned four Good Old sailboats, all under $15,000 (LeComte 33, Bristol 26, Bristol 27, Caliber 28) and the tough part about Good Old boats is that the value is often tied to the condition of the engine. You can spend as much for engine repair as sail and
rigging repair and why? Can't sail that well?
If you can't claw off a lee shore under sail, you are dangerously dependent on power. Certainly I want to use an engine in harbor, but with my limited wallet, I'm not going to waste money on a useless powerplant. If the inboard dies on a sailing trip, you are beholden to whatever mechanic you can find in that town, and they know it. If an outboard dies, pull it out, ask the locals about the best repair shop in the county, get a taxi and you've only lost a day of sailing. Buy a quick 6 HP, if you must, and continue your sailing.
And, yes, I'm limiting my resale audience, but I don't sell my boats that often, and there are lots of sailors with similarly-thin wallets and similarly open minds. I'm not worried.