"303 Aerospace Protectant" (available at Canadian Tire, etc...) is really nice for tires, dash, trim, etc. It's more of a matte finish but has good UV blocking properties which definitely help prevent tires from turning brown.
I personally use that every time I fully wash/wax/detail my car (about once every 6 weeks in summer), and am working on the last bit of Simoniz Midnight Black tire gel that I have left, using that every other week or so in-between the 303 application. The gel gives a really good wet look, lasts about 10-14 days, and I still retain the UV blocking of the 303.