I like Glock's 3.5 connector. I don't see a problem, as the trigger is still heavier than a "carry" 1911's four pounds or so. I disagree with those who's solution to a mediocre stock Glock trigger is to make it worse by increasing the pull. But to each his own.
I've lightly polished the appropriate internals of my G17 with a Dremel tool and a felt wheel using Simichrome - that helped a bit. (DON'T use files, stones, sandpaper, or lapping compound unless you really, REALLY know what you're doing!)
If you go slow, and don't remove enough metal to "reshape" the parts, it's hard to see how you could screw it up using this method.
I also added a Glock extended slide release. Doesn't really make much difference, and I'm thinking it may actually get in the way.
As far as other than Glock aftermarket parts are concerned...I don't have any. Many of the malfs I've heard of can be traced to non-Glock springs, recoil rods, firing pins, and trigger components.