I did not take apart the top end because my leakdown numbers were excellent. So the base gasket leakage is a 100,000 mile side-effect.
If I were to take the jugs off to try and seal the leak, I would use Hondabond HT on the gaskets. It is flexible, seals large gaps, and is the only glue that stopped my LC4 Duke motor from leaking (cambox).
Since you already paid for rings, and you have the base gasket leak... I would say go ahead and service the top end. Hone or otherwise de-glaze the cylinders, lap the valves, use modern chemistry to stop the leaks.
As long as your valves/seats are not cupped too badly and the bores don't have terrible wear.... rings and a valve job should be a big improvement. You mentioned that you think the bike is down on power... checking the leakdown is important, but you might also have more simple problems like valve clearances, carb settings, or even simply spark plug wear. I didn't read everything so I don't know the maintenance history of your bike, and all motors need at least some care. Is your air filter fresh?
I simply can't believe how fast my bike is with this many miles. I had a Honda Superhawk that was quicker off the bottom, but this 950 makes me happy every time I wind it out. For sure, it can't last forever, and I'd be a fool to take it to the boondocks alone, but I don't feel like it is anywhere near its end.