If you're wanting to stay in DXB on the free stopover, the only hotel they offer is the Bonnington Jumeirah Lakes Towers - hardly worth making an effort over. Note this is a different type of offering to EK's Dubai Connect - they will give you one or two nights free when you have inserted a proper stopover into the ticket.

http://www.etihad.com/en-gb/plan-and...ium-stopovers/

Making the 15 hour stop into a >24hr stopover will do two things: 1. If your fare does not allow stopovers, your fare will increase a lot; and 2. You will become entitled to chauffeur upon arrival and departure at AUH, which you will not be with a 15hr transit. The chauffeur will drive you up to Dubai, or indeed anywhere within the UAE.