I used to think this was true always, but on this past trip, we got stuck in the first 2 seats on Splash at the beginning of the day, and when we got off, it was like I had jumped in a pool. (I was in the front seat.) The next day, we did GRR and got far less wet. But we didn't get the geyser, so we were lucky!
I've never tried the poncho method, but I wore exercise type shorts (quick drying) and I changed into cheapie flip flops and stuck my sneakers and socks in my backpack before going through the line for both rides. My feet blister very easily and I cannot walk around in wet shoes and/or socks and expect to make it through the whole day. I was wet for awhile, but it worked ok.