In some ways yes, others no.
RS Guitar Works packages some relatively common parts (which are good--no complaints here!) and then upcharges. I've seen "kits" of parts anyone can buy for maybe $10-$12 selling for $50. They rely on the fact you don't know where to source the parts yourself...or want to buy a roll of wire if you only need a few pieces. Again, the parts are good. Magic? Probably not.
About "better" pots/caps/wire:
Pots: I'm more concerned with 1) does it fit the space required, 2) is it reliable, 3) does it "feel nice" when turning it, 4) what value it really is when you read it with a meter. Sometimes people will use a 350K pot and go nuts about how magic it is, when all they wanted was some lower peaks from their humbuckers (compared to using 500K pots)...whether they realize their pot reads 350K or not. If the sweep isn't perfect, it's easy to compensate for in most cases by wiring a resistor between pins 1 and 2 (not the 3rd "ground" lug), whatever value is appropriate. Or a bright cap, with or without a resistor in series. Anyway #1 is basically the most important because you can't compensate for that. #2 is good in the long run (not that swapping a pot is horrible, but it's annoying). #3 is a picky thing and I usually don't care much unless it's either flopping around not staying on full, or feels really stiff. As for the "sound" of various pots: other than its value and its sweep, I don't hear a difference. If there's a pot which keeps series resistance in the circuit when it's "full up", that would annoy me. Maybe I haven't had the displeasure of using some "bad" pots, to discover something like that (which I know is possible).
Caps: Changing them can make a difference. Changing the value is more important than changing the type/brand. Once you know what value works best for you, the rest is secondary. As for what's "best", it's subjective and a relatively small change most of the time, so I can't recommend one type over another (as long as you're using some kind of poly film or metal film type, anyway; I guess some guitars come with crappy caps, but I find lots of manufacturers supplying their guitars with plastic film caps these days).
Wire: I hear no difference in different "kinds" of wire.
That is, if they're all copper/tinned wire of the same gauge. Some want a "vintage look" with the push-back jacket wire, I prefer to strip the wire and not have frayed bits of crap in my way.
Solid core stays in a particular shape (when bent) much better than stranded, so that's something to consider, depending on what you're working on and/or how you prefer to work.
That's my 2c.
