I have the PV cover and jetting on my 250 but also installed it and tried it on the 2002 200. I am naturally sceptical (and a believer that stock is usually best), so did just the jetting first, tried it, then added the PV cover.
On my 250 the jet kit wasn't a huge improvement, but crispened up the midrange a little, maybe :think: . The PV cover made a pretty significant change in the bottom end though.
On the 200, the jet kit alone made the bike much "punchier" in the midrange (pretty dramatic change too)...almost MX like. Fun, but not as nice in tight woods. When the PV cover was added it boosted the bottom end up, so there was less of a transition to the midrange and smoothed out the "hit" or punchiness.
The power valve cover seems to work very similar to the older style Honda CRs, in that increasing the volume helps improve bottom, but likely sacrifices some top end (although not terribly noticable, to me at least).
If you like a punchy motor, I would suggest the jetting kit alone. If you want basically a little more or what you already have, go for both. I found the extra bottom/mid with both allowed me to run almost a gear taller in most places.
As I said, the "jetting kit" is mainly a special needle (seemingly leaner). In fact, I found on both bikes, that the main was too lean for our conditions, as the kit comes. I am still sorting out the jetting on my 250, as it is still not perfect with or without the "kit"