Good to see your message as you are trying to achieve the same goal as me.
I have short listed these two based on the reviews from Trip adviser.
Four Points by Sheraton Barcelona Diagonal
AC Hotel Sants
Both are in different locations and they both have pros and cons. Not sure either which location will be better.
Four points requires 50,000 points per night and AC Hotel requires 35000 points.
I am not sure as yet which one to pick. I will also review your recommendations as well.
Lets see if some one provides us feedback....