I can't comment on the Grosvenor, but...
My mother just came down for a 4 night stay to visit me. Since it was just her (my father couldn't make it) she hates spending more than neccessary for a hotel room. I usually set her up at the All-Stars, but they were all booked up. So, reluctantly, I got her a room at the Best Western.
I do have to say, it exceeded my expectations. It was a nice hotel. The room was clean, and in good condition. My mothers only complaint was that the A/C fan was a bit loud, and came on frequently. I got a rate of $41.95/night, and for the money, it was a great deal.
Although, I would still keep a Disney resort as my first choice, I'd have no problems having my family stay at the Best Western Lake Buena Vista.