i have a set of 17" all season tires (H rated) that are like new.. 90% tread. a tire shop guy told me that if i want to drive in wintertime, i should definitely get the tires "siped". does siping really help in snow traction? or is it a waste of $.. thanks

 

Siping are very small cuts in the tread. Siping is for rain, it is more commonly called "rain siping"....
If you want something good in snow, get some snow tires, Bridgestone Blizzak are pretty nice.
You won't really find many (if any) good performing (snow/winter weather) all-season tires in 17", just your basic H-rated run-of-the-mill all seasons.
If it were me, I'd get ahold of 2 more rear rims, and get some dedicated snow tires. Then you can just swap your rears with your snow ones at the end of the season. Just my $.02.