How deep are the pits, how thick is the metal ? Are the pits really that bad. In my experience of welding rusty cars, blobbing weld in to a rusty pit will blow a hole right through. Maybe better to leave alone.
I didn't see any anodes on your pictures, what do they look like ?
When did you last dock and repaint (at least two, pref three coats applied over several days after a full pressure wash and wire brush scrub).
Anyway,
Aside from that, most boats over 20+ years, need or have had some overplating. You can't stop the corrosion, only slow it a bit. If you're near salt water, or where there's lots of air in the water (downstream of a lock for example) corrosion increases. The bottom plate is usually better preserved than the water-line beacuse its the air that does the damage, tho' the bottom will get scraped on the mud more than the sides.
We had a full side skin up to the waterline done on a 28 y.o. 60 foot boat a few years back for about £8K. This was the last job this yard did before the owner retired so I can't make any recommendations now. This re-plating was forced by the BSS exam where the "examiner" hit the plates with a sledge hammer and he then made his judgment on the basis of the "clang" and the size of dent. Not very scientific IMHO.
I'd say that a boat which has had the work done will be more marketable, than one where there's an embarrassed silence or shilly-shallying in answer to the question "has it needed any re-plating".
You're choice may of course be limited to boatyards reasonably close to you.