If I decide to purchase 4 rims, there is now the added expense of that new law that requires tire sensor guages to be put on each tire... This would cost me about $720 total...

Obviously, it would be much cheaper to just switch out my summer tires and use the same rims...

So my question is: Is it bad for the tires to be taken on/off year after year... does this affect the quality and life of the tire?

Which is the better decision?

You are not considering the substantial cost to mount and balance the tires before winter, and again after winter.. then again the next year, and the next year... and the next. Because unless you drive it to death.. you will get 4 or more years out of a set of winter tires.

You are better off buying a dedicated set of rims for the winters as well as the TPS. It IS cheaper in the long run even without factoring your time in the waiting room every time

You don't need pretty rims in the winter....save the pretty rims for summer, they are going to take a beating in winter. And shop around for the TPS...prices vary significantly depending on where you get them.

Besides mounting and dismounting them 8 times over 4 years....more if you don't drive a lot of miles...WILL take their toll and make leaks at the beads MORE likely.

I use the 4 year figure because I drive an average amount of miles a year 10-13K per year. and I get 4 season out of a set of winters before I feel they are too badly worn that traction suffers....which is long before most people will discard them.

Separate rims.

Separate rims. You can even do the change yourself at home. The price you will pay over the life of your tires to remount them in spring and fall will cover the cost of the rims. It is just the smarter thing to do.

Thanks guys! Separate rims, it is!! I love experts!

If you have an older car, get the rims at a junk yard and permanently mount the winter tires.

TPMS Warning Light? Replace your TPMS Sensors for Cheap (http://www.stevejenkins.com/blog/2014/11/tpms-warning-light-replace-your-tpms-sensors-for-cheap/)

New law? REALLY? Does it apply to all cars, all years, all tires?
My last car had a broken sensor module and I drove it that way for years.