From my own experience this is what I think the optimum upgrade down the road is: Btw I bought my 2010 brand new SJ exactly 1 year ago and I have pretty much put all the mods available for it.
1. Steering... Absolutely number one for this ski. Post 08 SJ have shorter steering cable and they turn horrible. For that, you need a/m cable as the stocker is garbage. Get Cold fusion steering system. Its the cheapest and most reliable. It uses stock bushings and its awesome. Get riser bars as well and cut your stock chinpad to fit for the new goodies. after this mod your riding will improve drastically and you will have much more fun just riding around.
2. cut your riding plate flush with the hull and shorten your stock pole, make urself a limiting rope.. all its free and easy
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3. Bilge pumps. Its a must!
4. Turf and foodholds. The stock turf is concrete and horrible. At this point you will be able to make nicer jumps and first trick submarines
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)
5. Intake grade
6. B-pipe... this is the first pricey upgrade, but it will open the braap of your ski to another level
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7. ADA head
8. hooker prop
9. MSD enhancer
The rest is up to you: Engine keepers, a/m hood&nose piece, reinforcing the hull if you ride surf.