Without being snarky - and specifically based on your intention for this vehicle to run forever, a truly admirable ambition:

Let's be systematic.
a) You have confirmed a weak spark - yellow, and failing over a short period of time.
b) You have completed a maintenance task that while perhaps not 100% necessary is at least not a wasted effort - replacing the fuel filter.
c) Re-soldering the fuel-pump relay lugs is a good thing, again even if not absolutely necessary in hindsight - although if it cures the issue - all the better.
d) Next step would be the ignition control module/coil/distributor system. You may test the coil separately:

https://honda-tech.com/forums/attach...cture_3395.jpg

Or, purchase a complete assembly with all of it either new or reconditioned. I would hate for you to have to do more than what is necessary to effect the cure. Either way, a weak spark does suggest a coil - about a $15 ordeal from Amazon.

Peter Wieck
Melrose Park, PA