I've stayed @ Es Vive a couple of times, you'll like it for the fact that it's just full of clubbers, no kids and families which is always a bonus. There is a 24 hour bar altho that has moved indoors now due to sound restrictions. It's a great location as well, walking distance to Ibiza Town and PDB.
On the downside the rooms are pretty basic, way overpriced for what they are and cos it's a hotel there's no fridge/living area/etc in room as you'd get in an apartment which drives me mad for a longer stay but for a long wkend like you're doing it's fine.
You get a basic breakfast included in the price which is pretty nice and you can buy food round the pool during the day/early evening and that's always been nice. The pool area is nice but a lot of it is in the shade so if you're planning on sunbathing there get there early and get a sunbed in the sun.
There'll be plenty of people around the time you're going, loads of people go in September for Closing Parties.
If you do a search for Es Vive on this site you'll find more info about the hotel.