It seems to me that you are WAY overthinking this weekend trip. Although the reviews are sparse, they still give an indication of what to expect. My guess is that the raft guest house will be rather rustic but at 1000 baht or less it should be fine for one night. I've stayed at a raft guest house near Chiang Mai and it was much like the reviews indicated - i.e., you will probably experience some insects (and/or geckos), the bathroom will probably be basic (and the shower cold), and the room may smell slightly musty. But seriously, what's the worst that can happen? You sit on the little veranda in front of your room, have a few beers and some good basic Thai food, and unless it's pouring rain you will have some nice photos and a story to tell your friends about how you stayed at a floating guest house.

As for elephant camps, most of them are quite interchangeable. You've seen one, you've seen most - elephant ride, elephant show, and maybe a bamboo rafting ride. Each tour desk will have it's own preference (based on who's paying them a commission). I recall someone telling me that they enjoyed their visit to Taweechai elephant camp but I've never been there.

EDIT: I took another look at the Tara Raft listing and note that it's much more upscale than the floating guest house where I stayed. For one thing, you could only get to the place I stayed by longtail boat. Still, we had a lot of fun. But a riverside room with aircon, flat screen TV and free wifi - I don't see much reason for the hesitation.