For me, because it is always around my birthday, I treat myself and stay at the Hacienda. It has its ups and downs (many of which are chronicled here). One of the big ones is that it is fairly expensive or at least more expensive than the ones that are most used for the Weekend.
For the dinner, I always felt very comfortable wearing resort wear, i.e., a nice shirt and pants. Anotherwords there is no problem with khaki-sort of pants and polo (type) shirt. During the day things would depend on what you were going to do. I like to walk around town and go into the small stores. I felt entirely comfortable in a casual top and shorts with decent and comfortable sandals. The second day is the pool party and that is entirely for you to decide. I based my choice on my shame factor. I just brought a T-shirt and a nice pair of swimming trunks. But others at the pool chose rather skimpy bathing attire and with the bodies that they have I am very glad that they did. At the resort I generally stay it is swimsuit optional so that is one less thing to bring if you do not intend to wear a bathing suit at the pool party.