I love it, but then I'm biased owning a '79 estate
A lot of the things you mention are 'service' items such as shocks and exhaust and the 2nd hand spares availability (& price) is excellent.
You could find some good used front seats (I bought leather ones for £50) have the HG replaced and oil leaks sorted at the same time and get the welding done and you're halfway there.
Regarding economy, I fitted a 5-speed and Weber carb which has seen a huge difference!
As for modern cars being cheaper, we just discovered our V50 needs a new turbo - £800 for the parts alone!! Be under no illusion, running modern cars is NOT a cheap affair.
However, if you want (and are under pressure) to sell, the earlier models like this are getting much more attention and seem to go for ~£1000 for an MOTed example like yours. A start price of 750 or so would see some bidding action.
DO NOT SELL TO THE SCRAP MAN FOR £150!!!