I'd never consider a rain jacket or fenders. You are right - your jersey will get almost as wet from sweat than from the rain. I haven't had a dry ride in the last 4 days, so I hear you. What is nice is the isolated showers will cool things down a good 5-10* and is very refreshing. However, when lightning starts banging around I get to the point of wanting to look for cover. A recent storm killed 16 cows with one strike. After the wet ride I always do a quick wash, dry, relube.