I've not yet stayed at the Centro Historico hotel, but can comment on the Maria Isabel.
I have stayed at this hotel probably 50 times--almost always have booked a Towers room. On probably 50% of my stays, I have been upgraded to a junior level suite. These are superb!!! The exercise facility is nice, plus they have two tennis courts as well. The restuarant is pretty good, though I prefer to go to other restaurants around the city.
The last two times I stayed there (last month the most recent), my gold card had expired--but I got the upgrade anyway.
I will try out the new hotel though. Best of luck.
[This message has been edited by Ski Ag-'82 (edited 06-23-2003).]