Brawn84, all the upgrade kits you're considering so far are pretty good. I've got much of the same ones, and yeah, if you had the get only one, the Fansproject G3 trailer is truly the kit to get.
This late the in the game though, you'll be hard pressed to find good upgrades kits for CHUGs still, not just in terms of availability, but also price.
Beelzeboss used to make a pretty good G1 accurate head and weapon kit for Cliffjumper as well as another one to turn Bumblebee into Goldbug which fits perfectly if you have United BB.
I remember Perfect Effect used to have a pretty good kit for ROTF Bludgeon:
https://www.youtube.com/watch?v=3yqdoSvntRU
SXS also used to make a badass battle-axe/mace and a sword and shield combo:
Corbot-V's axes are still readily available and come in a few different colors. They seem to re-appear at TFCon every year still for the last couple of years at least.
https://www.youtube.com/watch?v=o9idt5Ed4xU
If you own a Classics/Henkei Nemesis Prime, a nice companion figure/kit to get is made by TFC they called Nemesis Primars. He's a cute little SD figure, but what's cool is that the jetpack he comes with is compatible to clip onto CHUG Nemesis Prime.
If you pair that up with the black MGS God Sword kit or Perfect Effect TAW01-B (not to be confused with their current upsized version PC-13 kit they made for Combiner Wars), then Nemesis Prime looks absolutely menacing all armored up.
TFC also had some kits that were very character specific. TFC-004 Gear of War is somewhat still available. It has a ladder upgrade for Voyager Inferno, and shoulder mounted rocket launchers for Sideswipe, Sunstreaker, and Mirage as well as a little scout/drone that folds up into a tape. The other kit, TFC-005 Gear of War 2 is really hard to get now. It was a set of G1-styled Optimus Prime rifles with blue LED's in them, one was for CHUG Prime, one for Alternity Prime, and 2 for leader class movie Prime.
Dr. Wu used to have a number of cool swords they used to make too but they're harder to come by now. Skybreaker, Tyrant, Prime swords....they were all pretty nice. Their Prime swords were kinda heavy though since they were made purely of die cast metal so not every figure could how them if they didn't have a tight elbow joint to support the weight. The other 2 sword types are translucent plastic though and held up just fine.
Renderform (venksta on the boards here) has made some pretty good melee weapons in the past too, but they are of course limited production. Currently, he's producing guns for CW figures, but they're all 5mm peg compatible so you could give them to almost any character really.