I never owned one of these, but I just read somewhere that the tensioner spring should be replaced as often as you gain access to it (on belt changes) because YES, while it is part of the tensioner assembly, it can fail before the other parts do, and cause the chain to eat the world around it (or something like that). In other words, it was a really cheap insurance policy to prevent a pretty expensive disaster if it ever failed. (The spring pushed the plunger which provides tension against the chain? That's how I understood the article).

ALSO, if you're just dripping with spare money and need good places to spend it, smarter people than me have said it's wise to always keep a spare gasket kit on hand. If something pops in your car, and your local Nissan dealer doesn't have the correct gasket kit (or isn't open at the hour you have the trouble), having a spare kit saves you waiting for UPS delivery from Rock Auto or something. It might be a simple thing like a thermostat gasket, which you could change in less than an hour *IF* you had a gasket kit available. Otherwise, your car could be sidelined for days, waiting for a gasket kit to arrive (at emergency delivery price). Gasket kits don't have shelf lives ~ you can keep them forever in your garage until you need them. But it's far better to have them and never need 'em, than to need 'em and not have them.

If this was my car, I would go to Rock Auto and see how much the Gates timing Belt Kit cost, if it comes with an Aisin water pump. Or get the timing belt kit and an Aisin water pump separately. The kit should have the tensioner and spring with it, but yes, I would replace all that. I wouldn't mess around with that, don't want any issues down the line. I forget if there is an idler pulley, should come with kit, but replace all this old stuff. Cam and crank seals are a givin, but never seen them leak, but might as well while in there. I'd go Beck Arnley on those if possible. I use permatex on the outside of seal when I install to make sure they are permanent. These are all reputable companies, and I probably been using them longer than you are old.