To me I think GRR is kinda a crap shoot if you get wet or not. I have seen people walk off with nary a drop and others drenched. It just depends on where you sit and if you get lucky enough to have a geyser go off next to your seat.
On Splash, now that's a different story. It definitely matters how heavy your boat is. If it is filled with adults (tall and decently weighty), then the boat sinks lower into the channel and water can more easily spill into the boat throughout the mini dips and just the average rocking around. 2 examples for to keep in mind. I went with DM, DF, and DB a few years back. We are a very tall family (DB is 6'8" and DM, who is the shortest, is 5'10") and none of us are skinny Minnies

. They put us 4 in the front and a poor father and son in the back seats. We sat down and you could see the log just sink about 2 inches

. Poor DM came off that ride sopping wet; her shoes were sloshing and she ended up having to buy flip-flops just to dry her feet off.
Another example was 2 Thanksgivings ago, went with BFF's family. Again the 6 of us were all pretty tall. They put us all in the same log. Poor BBF's sis came off that ride soaking wet. She had to step into the bathroom to take her shirt off and wring it out over the sink. Poor thing had to buy new pants because her jeans just weren't drying off and were actually starting to fall off of her because of the weight of the water. It was ridiculous.
So in conclusion if you have made it this far, GRR, there's really no way you can plan on how to either get wet or not to get wet. I would just expect it. On Splash, make sure that the weight isn't too much for your log. If there are a lot of adults in your party, I would suggest splitting up or generally just making sure that you won't end up like the poor father and son that were in the back of my family's log.