removing the baffle will not require a jet kit, but it may require you to re-jet. Depends on your elevation and temperature. (You should be able to buy the individual jets you need from a local dealer for about $5 a jet.). A jet kit will help give you better acceleration, especially off of the line. If you were wanting to do that, I haven't paid attention to any of them other the
JD Jetting. But for Polaris, their options are very limited. But the golden key to their great kits is their needle. If you could just get a needle that fits your carb from JD Jetting, thats all you really need. It may be worth asking them.
Lowest cost clutch mod would probably be changing out the primary spring in the primary so that you change the engagement to happen faster. Unfortunately, I do not have a chart to look at, so I am not sure what to recommend, but the different spring rates are coded by the color of the spring. Your local dealer should be able to pull a chart out of their service manual to help you, or maybe someone will know off the top of their head what color spring to go with.
Are the plugs wet? You didnt say if you are using the oil pump or pre-mixing, but either way, you are probably way to rich on oil and it is fouling the plugs fast. Usually it is excess oil that fouls plugs out.