Interesting to read this, especially as I live about 10 minutes walk from the Marriott Maida Vale. While I don't know a great deal about the property, I would like to add a few local observations about the area. The Maida Vale name is somewhat cheeky as the property is most definetly in Kilburn, and as noted above, Kilburn is a very diverse neighbourhood. It's fairly safe, but I would advise being careful late at night on the route between the hotel and the tube. There is some drug dealing in the area and with that comes the usual petty theft problems. There is a great pub in the area called the Clifton (on Clifton Hill, a 2 minute walk. Relaxed atmosphere and some great British ales. Buy me a pint should you find me slouched at the bar!
While the Regents Park is a cat 6, the area is a bit more relaxed/civlised and only 3 minutes walk from Swiss Cottage tube station. There is plenty to do in the neighbourhood too.