If you have a card like Plasteel staff equipped with [surge]: +1 [damage], can you trigger that more than once if you have multiple surges?

You may not. A surge ability can only be used once per die roll. Though if you have two separate surge abilities that do the same thing, you can stack those with multiple surges. The Force Pike, for instance, has two [surge]: +1 [damage] abilities.

Thanks for the prompt reply!

Any ability can be only used once per timing instance, including surge abilities, also the innate hero ability to recover 1 strain by spending one surge per attack. (Recovers damage if strain could no tbe recovered.)