Heya,
1. I haven't been since the dam, but it still probably worth going. Play is unbelievable, and there are plenty of rapid even without the TotalGanga, SurfCity and Silverback (mmm... getting goosebumps from the memories
).
2. You'll be fine with lycra for most days. A short-sleeve top is comfortable for rainy days, but not a must (can get a bit chilly, but you'll survive without).
3. I always stayed at NRE, don't know if Eden is handy for boda-boda (local motorbike shuttle).
4. Just think with you head, try not to get malaria (trust me, it sucks) or AIDS.
Enjoy,
Dima