I actually lived in Yaguate and went to San Cristobal at least once a week. There isn't a whole lot I think tourists would be interested in, the Cathedral was built by Trujillo and is somewhat interesting, up on the hill is another one of Trujillo's mansions, it is 5 stories tall and overlooks the city. The military have a few guards but if you pay them 500 pesos to help with upkeep you can go inside and look. It is pretty big, and is very much a "haunted mansion" type atmosphere. There are even bats in this abandoned place.
Another intersting things to see is the beach at Palenque, it is probably the best beach in the area but probably not that great compared to the east and north. Around there are a few hotels I think. If you want to get off the beaten path and see something really cool, I suggest you talk to the locals and past Yaguate by the river Nizo I think, up that river is a dam but the river is perfectly clear and great for swimming in some parts. There is also an amazing waterfall where a small river passes through two giant rocks where the Voodoos have a little alter in the rocks. I forgot what exactly they call it, but it is probably one of the most amazing things I have seen down there. I actually went with some of my Dominican friends, they road a bike and I road on the back of an old motoconcho up the sometimes dirt road. There isn't even a road to get to the waterfall, but if you ask around enough I think you can find it. Actually once we were done we tried to walk back the 5 minute walk a different way than the path we went in on and ended up going around in circles in the jungle for a couple hours.