Moving to 17" wheels will not affect your wet/inclement weather handling. It will all depend on what tire you are running. In fact, since the proper tire for a 17" rim would fall in the 40-45 sidewall range, you may lose all-season tire options. The only "need" to get 17" wheels is to clear big aftermarket brakes - all the other reasons come down to personal preference.

I found a cheap set of Volans for my T5 - basically the only reason I have 17" wheels on the car. I like the way they look, too.

For your needs, I would recommend spending money on better tires than on new wheels. Do some research and find a good all-season. Or, if you plan on seeing a lot of snow, get some good high-performance tires for summer fun and a set of snow tires for the winter.
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'99 S70 T5M, '83 245 DL