If it works, leave it alone.
The alternator belt on my boat is well beyond its 10th year, the impeller 25 years, the engine hoses 30+ years.
If they look or sound distressed, they get replaced, not before.
There is no way on this earth I would change the belts, impeller, or hoses on a motor that had never been used.
Run it first, see how they perform, see how they look, then decide.
You might want to re-think this one. Parts wear out, but they also degrade with age. An engine hose at 30 years? Unless you are really careful in checking them, you might be headed for a failure. A failure, by the way, could cost a lot of money, or happen at a time when the boat could be placed in jeopardy. But, if you're really on top of checking them.... An impeller, however, cannot be checked unless you take it out - at which point you might as well just replace it. An impeller that fails can overheat an engine really fast.
I'll illustrate my point with two stories:
A friend at the harbor is a really good sailor. Nice boat too. He came back in after a daysail with his mast broken in two. Turns out that the turnbuckle failed. Older boat, hardware older than the replacement schedule. I saw the turnbuckle. Where it failed, it was rusty along the failure surface. In other words, the failure was a long time coming. Not an engine failure, but a failure that could have killed someone if luck had gone against him.
Second story. Friend's boat, different friend, engine stopped. I towed him in. He cleaned all the filters and went to his boatf the next week, but the engine wouldn't start. Turns out that a bunch of crud had blocked the intake tube inside his diesel tank.
My point is that you don't have to go crazy, but you do need to maintain your boat systems. At least replace that impeller. In my experience, it pays off to do filters, belts, fluids, clean it and look for anthing else that you can do. A stitch in time saves nine.
Just my opinion, and how I run my boat. Your boat, your choice.