The cost of parts isn't dirt cheap, but tube amps of any ilk aren't cheap these days. It's not a bad idea to spend $30 or so and replace all the parts on the driver board. Then either use one of the pre-made power supply boards or build one up out of perfboard (yes, the guy who profits from your driver board purchases is suggesting that you use perf-board...). The power supply caps are about another $40 or so. This will get you in a place to objectively evaluate the amps (you wouldn't critique an antique car's handling with 40 year old tires on it would you?). And I'd bet you'll get every penny back out when you sell them (unless you really goober them up). And going to the stock topology with modern (non-tired) parts will give you a good baseline for making other mods if you choose to.
Sheldon
Sheldon