Riu Playacar has stopped the long pants for dinner thing about three weeks ago. We just got back and people are wearing just about anything (some look worse than they would to go to the golden arches at home).
If you don't like your seat at dinner, you can request another, they have more than enough open tables, even in high season.
Air conditioning can malfunction due to the magnetic switch on the patio/balcony door. Our A/C wouldn't work at all until I jumped the switch with a piece of wire (next day, I put both wires under the same screw; situation resolved.
Riu knows they have a musty smell problem and their solution short term (they won't tell you this, they just do it when you are out of your room) is to put coffee grounds in a glass somewhere in your room. I don't think it works as well as they think, but it helps.