I have used and experimented a variety of these. I bought a lot of local POTs and recently I also bought myself a handwound special CTS POT. There is a noticeable difference. Now the sound is more clearer and has more gain and treble even with the same value of resistance. I have also tried a few of the local input / output jacks. I wasn't much happy with it. There is a lot of leakage and also the production is also not very good. A few of them dont fit snugly. So I imported some 50 switchcraft jacks. I got such bulk numbers for a different reason. These are surely expensive. It costs about $3 per jack as opposed to Rs.4 to Rs.10 for a local input / output jack. If you are worried about that small difference, then you shouldn't look at these small compromises. I know some real guitar experts who say that the $350 Ibanez RG is almost 85% as good as the $2000 Ibanez guitars. It's that remaining $1650 which gets you that last bit of 15%.
I recently purchased a few 12AX7 Vacuum tubes. Here they are available right from Rs.90 for a BEL manufactured one to about Rs.180 for RCA tubes. Every bit of electronic components do make a large difference. If you are an electronics hobbyist then buy two sets of components from two different makes and rig up the same circuit and see the difference yourself. There are lots of articles on the web available to tell you which make of Tube will sound which way. I have seen analysis of this.
Same with cables. Do an AB with two cables and see the difference yourself. A lot of treble gets cut in our cheap cables. A lot of noise is also introduced.
I'm the one that has to die when it's time for me to die, so let me live my life, the way I want to. - Hendrix
If you can remember the '60s, then you weren't there. - Unknown
I'm shopping around for something to do that no one will like. - Jerry Garcia
Don't compromise yourself. You are all you've got. - Janis Joplin
On stage I make love to twenty five thousand people; and then I go home alone. - Janis Joplin