Milkman,
It's a tough call to figure whether it's worth putting a large sum of money into an old bike.
I had my heads done in 1998, cost was around $500US, plus all of the other things I did, while I had the bike apart that far.
I just went through a costly maintenance cycle this last year, I put in just under $2000US into my '81 R65, with 80,000 miles on it, I don't think it's worth $2500US tops.
But I 'live' on my bikes, I ride to work just about every day and do a large portion of my errands on the bikes, on average, I fuel up the cage once every 6-8 weeks, (6-7 US gallons) and it saves wear on the cage, my '91 CRX just turned 100,000 miles, probably would have over 200,000 miles on it without the bikes.
So I guess you have to figure out for yourself whether the bike is worth the money and effort.
But from what I've read, most R65 owners regret selling their bike afterwards.