What year and model SlingShot do you have?
We added the vented Madstad windshield to our 2015, but that was before Polaris started venting their stock windshields.
Our MeanSling SportTop makes the ride quieter and less turbulent, and is reasonably priced in comparison. Oh, and the MeanSling hood assist does aid in opening/closing the hood. Aw yet another thing you may want to consider the MeanSling storage bags for additional space.
Depending on your location and riding climate, you may want to invest in better tires.
If costs are not a concern:
A rear fender adds a finished look to the rear.
Personally, for the prices available, we have found the stock shocks to work just fine, but the ones that you mentioned appear to be at least a lil more reasonably priced in comparison...................
If your brakes have been bled and operating correctly, there should be no need for an additional brace.
I believe that many would also agree that there is not much to be gained by going to a cold intake system.
Bill