I stayed at W Barcelona over New Years for 10 days. I had originally booked the cheapest room and got a pre-upgrade to a Cool Corner Suite. I contacted the hotel and asked about upgrading to a Marvelous Suite and offered 100E extra a night to do so, which they continued to decline. At check-in I asked about it and they said that since there was still available they decided to accept my offer for 100E extra a night to upgrade to it, and I got it for the entire stay for less than 300E a night.

There are 6 Marvelous Suites total, so they usually will NOT sell out of them at their standard rate. The thing is, the management will of course try to get you to pay more until check-in when they are not all occupied. So you can offer a relatively low rate and you will probably get it, but it is not guaranteed. But since they weren't even all booked over New Years, I wouldn't sweat over them not being available.

Also, another important thing to note is there are only 2 Marvelous Suites that are like the one listed on the website. The ones on the 21st floor have a much larger terrace and room than those on the 22nd and 23rd floors, so if you want that make sure you specify that. We originally were given one on the 22nd floor and it was not acceptable with what they advertised on the website.

Good luck!