The only thing that would increase performance from that list is the hop up unit + rubber.
Also to the best of my knowledge there aren't any terribly *good* drop in V3 mechboxes (supposedly the "Action V3 drop in gearbox isn't that great) so you're probably going to have to get a shell + parts and assemble one, however due to fitment/tolerances between different aftermarket companies this may prove to be a headache (they will always have the right tolerances for Tokyo Marui OEM plarts but may not play well with other aftermarket brands parts).
I myself quoted the price of a V3 mechbox with all Prometheus parts and a gearbox shell and it looks to be ~$350 USD however you may have better luck finding good deals for these parts and such.
From your list though personally speaking I would say drop the hop up rubber, nozzle and spring guide. As for the wire and connectors you may have better luck at a RC hobby shop or electronics store. I know you can get a bag of deans connectors for ~$5 and the wire can really be found from a local electronics hobby shop or even your local high school (if you have any friends/siblings in school or know someone who does work with electronics).
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE