Ditto. My first two trips to Vegas, we stayed at Bally's; once for a great rate and the second as part of the package. Both times... view of the roof/parking lot.
Ever since with the $20 trick, I've been booking the cheapest rooms I could find and getting upgraded to high floors with great views of the strip, fountains, etc. It's only a quasi upgrade as it seems many of the hotels charge a bit of a premium for a view room.