Is it worth it to pay extra for a stainless steel tank water heater?
The key word you used is "theoretically".

Stainless steel is not all the same. Is it 304 or 316 stainless?

It should last much longer than glass lined but still not forever.

If you can afford it, for longevity, I would eliminate as much steel or galvanized steel as possible.

Good luck on your project!