How can you tell if it’s worth fixing? You usually can’t. Even seasoned harp restorers will warn you that a zillion hidden problems can lurk in the pedal mechanism, especially if the harp is an antique. It needs someone with a professional experienced eye to look inside the pedal box underneath, and even then most of them will only chance a cautious estimate. You usually don’t know for sure until you begin working on it what you’re going to encounter.
Also woodworm can do a lot more damage than is immediately apparent. Those tiny little holes can be masking a whole rabbit warren of tunnels beneath the surface, which means the neck or affected part can be considerably weaker than it looks. I once saw an old harmonic curve in cross section and it was so porous it resembled a piece of French bread! But all that was visible from outside was one or two tiny holes.
If you’re looking at something in an antique shop for a knockdown price, NO ONE is likely to know the true state of it, or where it’s been. Take a qualified harp restorer with you, and even then don’t expect anyone to commit him/herself.
If the pedals are FULLY working then you may be in with a chance. But how likely is that??!!