Keep in mind the resort is a good distance from Chiang Rai.... 3 nights is really perfect here. ... Perhaps an additional spa treatment. To be honest with you, I found the long tail boat ride and the city visit very lame. I skipped the Opiuim centre in favour of some pool time.
Ok, so the pool and spa were good, but not the adventure part. If added adventure is an additional spa treatment you could be anywhere...