I did the following mod to my son's 2008 Vector and it was a huge improvment. Remove grips, then carefully remove heating elements from the metal bars. Install a layer of cork on the bars, reistall heating elements on the cork, then install new grips.
It took my son and I one hour and the grips work great now. We had tried foam and handguards first with little benefit.
Having the foam ensures that the heat comes out into the grips instead of being absorbed by the bars.
I got the idea from one of the snowmobile forums, learned it was something they do at Nelson's Speedshop in Greenville, MI. Stopped at Nelson's, talked to one of the service managers, they got me the cork and grips ($30) and the rest is history.
Simple, fast and effective mod...