Yes, you should take the rain skirt. If you have to ask either you are either banking on it not raining at all, or you never tried it like that in extended rain. First of all, your legs get wet WITH a rain skirt. Unless you have an anorak or a poncho its not your legs, but the entire lower half of you body that is the issue. Your rain jacket will make this even worse since all the run off is going to run down into your..ahem.. crotchal area. While this might be refreshing for 30 minute during a 90 degree day, much less so for hours on end, and potentially very bad if it is windy and in the 50s. You can get hypothermia quite easily spending extended time in the low 50's, especially if you don't have enough rain protection to keep your core temperature up. At the very least have an alternate plan if it get chilly enough - some dry underwear in your pack will cover the entirely wet crotch issue, but then again they weigh just as much.
BTW, the stupid light extreme aside, the reason so many people like rain skirts is that they are more comfortable to hike in because of the ventilation - the lighter weight was originally an extraneous bonus feature, but it seems like a lot of people on here now think the whole point is to save weight.
A cut up garbage bag & duct tape will work just as well, and maybe you can get it down to 1.5 oz. Otherwise the modded driducks are a great, nearly disposable alternative to stupid light.
You should take a look at the zpacks poncho groundsheet (if you are going to the extreme of considering cuben) instead - replaces rain jacket and pants, groundsheet, and pack cover, and has better ventilation than any rain suit - ideal for the kinds of mild condition you are referring to. Also at the very least ifit is your groundsheet you will always get to use it every day :-)