In 1977 I bought a BMW R60/5 from a friend that was selling everything that was not nailed down to restore a ME 109 (for all of you that are trying to think of what kind of motorcycle that is ...it's not). That R60/5 carried me for quite a few years and through all kinds of weather and never let me down. Well scoundrel that I am I traded it in on a R80/7 and found that BMW had really cheapened their bikes. I sold it a couple of years later in discgust and went bike less for a year.
One day I was in the ware house of a kerosene stove / motorcycle distributer and looked back in the corner where a bunch of junks were stored. There was my old R60/5 in the corner even with the boat horn I put on to be heard. I bought it back for a song and keptit through 8 moves, rode it to bike week several times etc.
Go ahead and get the bike and ride it 500 miles a year just to remember how much better they are now.
If you've got money to p iss down the drain then go ahead and fix up your old friend. Maybe if you can find a cheap donor bike you can join them to make one whole decent bike. If you plan on buying everything new, you will find that Jap bikes have prohibitively expensive parts. The cost of fixing with new parts will quickly outpace the the book value of the bike. That might be the manufacturers' way of steering folks towards buying new instead of fixing perfectly good bikes. If you have money to burn then I say go for it.
I once had to fix my wife's 600 Radian carbs. One of the four was cracked and the cost of a new carb (just one of the four) was 350 bucks and I couldn't believe it. I went to a cycle salvage business and paid 100 bucks for the entire bank of 4 carbs and went home feeling great. Bike still runs like a top. Of course I had to set the floats and sync them but we're talking carbs not injection here.
Hogs are meant to be rebuilt forever and that is why, at least as far as I know, there are no Harley salvage yards. The closest thing to Harley salvage is what are called Swap meets. Jap bikes are great bikes but they change things so darn much and that is all marketing to make you think that the latest model is so much better than last years'. There are a few Jap models that come to mind that stay the same: Kaw Concours, Yam V-Max, Gold Wing. The crotch rockets are like mushrooms, new models sprout up overnite and then the next model comes out and you feel like you are riding an antique.
I wouldn't bother with it myself, the reality never lives up to the memories no matter what you're talking about. There's a few of the bikes I've had I wish I would have kept but for the most part when I sold them I was done with them.
The only one I wish I still had really was my Trophy which got totaled, I wanted to keep that one a long time but fate intervened unfortunately. I really enjoyed my Bandit too,but they're pretty easy to find so if I missed it that much it wouldn't be hard to find another one...
I had a GS650G the smaller version of the 850. It was a good bike, but boring and it buzzed above 65mph - I wasn't used to 4-cylinder bikes. Always wanted the 850 - back in the '80s - not anymore though.
The thing about fond memories is that they soften and mellow and become sweeter over the years. Don't spoil good memories of the time spent with a favorite bike by bringing it into the harsh light of the present day, where its faults will be glaring and the things you loved about it will pale in comarison with the virtues of current bikes.
Ditto on the rose-coloured glasses theory... I sometimes miss my NC24 VFR400R (and the owner before me occasionally berates me for having sold it to me), but then I remember how bloody awful it was to keep on the road when no mechanic this side of the Orient knew which end of it was up. And I never want to see a carburettor again in my life. Filter out the bad memories, keep the good ones, and move on.