I used to work on old Alfa Romeo's and our customers would bring in nice restored cars that didn't run/drive right. Reassembling and getting a 'restored' or 'show car' to start and drive is not the same as sorting it out so that it is a pleasure to drive. By 'pleasure' I mean that you aren't worrying about the 'next thing'. I figure, what's the use of having a car (beater/showcar/toy) that you can't just get in it and drive. Without having a towers business card in your pocket.
Fixing one thing and having to fix something else a week later is ok.
Fixing one thing and having to fix it again a week later is bad.
Usually, when working on old cars, if you mess with something, you will have problems with whatever else you messed with/moved. Things are happy where they are. Disturb them, they disturb you. But it is an easy thing to anticipate. Replace any rubber item (hoses/belts/boots) that is old and you have to remove/move to do a repair. Even if it is not related to whatever your currently fixing. And many things can be done at the same time: water pump goes out. Replace hoses/belts, front timing cover seal, have radiator cleaned, check lower radiator mount, check and replace alternator mount bushings, and clean. Clean everything. Since so much has to come out to do the water pump, the rest is just time and some extra parts. This is also something to consider if you are paying someone else to do the pump. Why pay someone to pull it apart two or three times for little things?
It takes a bit of planning and foresight to do this. And a little money. I'm lucky enough to have many spares (new and used), but I still buy certain seals, gaskets, hoses, just to have them on hand, rather than have to go get them/wait for them when I go to do something.
Another example is the clutch. If it is old and worn or getting weak, start buying the parts now. Get another flywheel and have it resurfaced ($40 last time I did it, less down time if it is sitting there ready to go), new throw out bearing, new pilot bearing, front/rear trans seals, new bolts for pressure plate to flywheel and flywheel to crank (at least two of each, never know what you'll find when you take it apart!), new seal for the speedo fitting. And while the trans is out, that's a good time to do the shifter linkage seals (requires a very simple modification to one shaft, but not possible in the car), thereby reducing the number of places you can leak.
All this rambling is me just trying to say that if you take care of something that you know is a problem before something happens, you will save time/money/mental anguish in the long run. And you feel even better about the car.