Having replaced the tanks on my 1985 Krogen last year I admit it is neither fun nor cheap. However the question of repair or replace gets even more complicated when you consider the eventual resale of your boat. Even if the repair is successful and lasts for your use of the boat, prospective buyers are going to ask about the tanks. In this market buyers have a choice in boats and may discount their offering price on your boat by more than the cost of the replacement. This is the old real estate situation of the guy who puts up with a leaky roof for years, patching the roof, repairing the inside damage and then when he sells the house having to pay for or install a new roof.
As to the issue of the second pinhole developing when I replaced my tanks it was the starboard tank that was leaking (slightly). We cut it out and could see the rust. When we went to cut out the port tank we started to remove the framing and all of a sudden the port tank split along a non-visible rust line and dumped the water in the tank into the bilge. Obviously the rust had affected both tanks.
Good luck with your decision.
Marty