Modern Vespa

Bike stored indoors since new. Very little use over the years. Am I way overdue for a belt change? I wouldn't know how to open the guts and check, as I'm not very mechanically inclined. Oil changes and other maintenance have been performed annually to keep it in riding condition. Should I be thinking of changing that belt?

When stored inside and little use I expect that belt will be OK.
I have more worries about the pulleys: will they slide as shood.

Take it for a ride.
And check how the transmission works.

17 year old rubber belt , yeah is due to be changed, also tires, oil and filters, especially the air filter as those crumble after just a couple years and you don't want that sucked into the engine.

I agree i would change all the oils, fluids and the belt. I wouldn't have any faith in the tires either.

what old as dirt said 👍

Shredding a belt sucks 100x worse than putting a new one on.

I wouldn't change either. Keep an eye on your tire pressure and look for cracking sidewalls. If the tires stay inflated, and there is no visable damage ride on. I'd lay money if you pull the belt, bend in backwards, look at it real close, it still looks like new. Are you running a risk of problems? Maybe, probably not. Spend the money on these items, 100% certainty your money is gone. I bought a 2009 BV250 last summer with 1,200 miles. I changed all the fluids, spark plug and filters. I didn't touch tires or belt. It now has 6,000 miles on it. I'll do the belt shortly and install DR Pulley Sliders. I'll replace the tires when they are bald.

No, you don't need to change it. Scooter drive belts are made of binder impregnated layers of aramid and/or polyester fibers. They don't stretch, lengthen or otherwise break down when they're not working.
Make sure there's still an air filter in the bike. Fill it up with fresh gas from a busy name brand station like Chevron or Shell, ride it through a tank or so, then change the oil, drain and replace the coolant and replace the brake fluid. When you change the rear tire, change the gear oil. To err on the side of caution, you could always change the belt 500 miles before called for, but you really don't need to.

17 year old tires enough said.

How long do you think motorcycle tires last?

I think ten year old tires are expired.

Most stuff has a double life/load built into it as a safety factor. Standard Engineering thing it has to handle easily half again what it is rated for.

If the tires look good you can certainly ride around to test stuff out but if it becomes your scooter and you start riding it regular you should think about new tires .

My Liberty 150 came to me used with low miles and needed a new tire at 4,000 miles. I Imagine if you are careful and try to ride gentle you could get way more miles on a tire but where's the fun in that?