I have had a lot of vehicles over the past 14 years of my driving career, and I have only seen the paint fade while washing with hard water (including lots of minerals such as calcium) or when I cleaned it by hand using cloths or chamois. Over the last few years only use soft water and rarely use soaps. I'm no specialist or anything, but normal usage means that dust will settle on painted surfaces and probably reside there & over the years it looks faded. Here in Canada, we don't have the heat that some others get in the southern USA, but direct sun contact will obviously harm your paint the most.

As for the heated seats - it takes energy to transfer power from the engine to alternator to heated seats, so it definitely will have some effect on your fuel economy. I don't think that it will make a real noticeable difference though if you only use it now and then. I used my heated seats along with the fan for heat and noticed about 2 m/g difference compared to the warmer weather recently.