FYI for the SPA trigger group, polishing the contact surfaces helps but the trigger blade has a ton of travel before it fires, and I got a comparatively bigger improvement by adding a bushing to the bottom pin of the trigger group. That took up most of the travel and made it much more predictable. People have used a variety of things for the bushing and you can probably improvise but I used a 5/32" aluminum rivet. Knocked out the mandrel with a punch (or suitably sized finish nail), kept the aluminum body, enlarged the hole with a #39 drill bit (so the 2.5mm pin will go through it), then cut off the flange with a Dremel wheel.
To reduce the pull weight, I took a spring from under the flint of a disposable cigarette lighter and cut it to the same length as the original (much heavier) spring.
Those two things made an absolute night and day difference.