About strings, yes I went back to nickel plated vs "pure nickel" before and there is definitely a difference in favor of the former regarding treble!!
And I actually went slightly down on guages (going from 11-50 Dr Pure Blues set to GHS David Gilmour signature set for strat in 10-48, very nice set indeed!!), that could also help to brighten up my sound.
I quite like this set on both the strat and tele. And yes, this should bring some brigthness back.
About pots, I'm considering whether to change only the volume pot to 500k or to change both for 375 (which both leads to a total resistance of 750k).
I'm not an electronic engineer but I don't think this is how it adds up :lol:
But anyway: I tried a quick simulation and it seems that 375/375 would give you a tiny wee bit more hi end - but don't take me on words here and wait until someone more knowledgeable chimes in.
And about treble boosters, I've never tried one!!! (I had many fuzz boxes, OD/Distorsions, boosters...but not a TB!!)
Can you advice me some please?
The all-times classic is the Dallas Rangemaster (or at least clones of...), which I never tried so I can't comment.
The Xotic EP Booster worked fine for me so far on Fenderish amps (Blues Jr, HRDx, DRRI, Silverface Bassman 50 and a couple Brownface and Blackface clones), Vox AC (15 and 30) and Peavey Classic 30 (clean channel, cranked). Didn't work fine on the Epi Valve Jr (which is kinda picky about boosters and dirtboxes) and doesn't add anything useful on the SLO-like channel of my (custom) amp.
I tried a couple others when I bought the EP Booster - Jacques Katapult, EHX Screaming Bird and at least another one I can't remember, all on a HRDx which was my current amp by that time -, and found the EP Booster to be the less transparent yet the more interesting. I really disliked the Screaming Bird (ice-pick anyone ?). The Jacques Katapult was far from bad but mostly a bit too clean to my tastes. OTHO that might as well be what you're after.