Thw standard repair advice would be to ensure it meets spec . Then to replace the all of the old electrolytic and the other caps as needed.
The value of an amp is only estimible for a moment in time, and for an amp of a certain condition. The best way I think to do this, is to watch ebay auctions through to the final selling price....not what is asked.... but what it selles for. If you follow several auctions you will get an idea of what people are willing to pay for that amp in a variety of conditions. What somebody will pay is what it is worth.
The value of an amp is only estimible for a moment in time, and for an amp of a certain condition. The best way I think to do this, is to watch ebay auctions through to the final selling price....not what is asked.... but what it selles for. If you follow several auctions you will get an idea of what people are willing to pay for that amp in a variety of conditions. What somebody will pay is what it is worth.