Well, you've posed several different questions. 1st, is it worth it to repair the OEM tank? Only you can look at it & know how bad it is. & you know your skill set... can you weld it safely & properly? If it's not rusty inside or out, it might be worth doing. 2nd if you can find a clean (inside & out) salvage tank... well it's worked for 20 odd years & as long as it's good & the install is done right, you're good to go! Buying aftermarket is touch & go, but I'll say that Spectra is a well known brand & I installed one of their radiators in my '96 a couple years before I sold it. It was every bit as well built as OEM & the only difference is it didn't have the OEM foam rubber on the top tank. I've no doubt it's still going down the road today.
Personally, if I needed to replace a gas tank, I might look into adapting the Petroworks Sammy tank into a Trackick. I've always wondered why they don't offer one specifically for Trackicks (at least last i knew)... I mean what's not to like... ABS = no rust... ever... very hard to dent or damage... comes with its own skid plate & provisions for all OEM connections including the fuel level float. A bit pricey? Yeah but it won't need to be done twice either.