Well, I would say it depends what the temperature was. When I was in the Czech Republic, the beginning of the tour was about 53 and rainy two of the beginning days. I very much needed my rain pants. I can't imagine riding in wet shorts or tights at that temperature. It would have to be at least 75 degrees before I could do that, without feeling hypothermic! I am talking about steady medium to hard rain, for hours. Sure, some of the others made fun of my booties, rain gear, wool socks, helmet cover, but you know what? I was dry and they were not. It was freezing to me... but of course, I also bring enough pairs of shorts for each day of the trip, which makes me the odd one. I guess being self supported, weight is an issue, but I don't think I could wear a pair of shorts that had been rinsed out in the sink.
I might consider those Gore rain shorts, which look cooler and easier to pull on and off.