(mostly?) Fixed my issues.
Took a chance on solving some horrid shaking from the trailer, that it needed springs (actually did the shackles/balancers/bushings/bolts already, but I like the new greasable ones) after ~25 years, and it definitely solved at least 95% of the perceived issues. I think that is point I'm just chasing "perfection" where there never was any, and am overall very pleased with the spring kit. If I need axles you guys will be my first port of call.