There hasn't been any fluctuations in Dubai rent, only increases!!
Peolpe who bought their own places 5 or more years ago have cleaned up. The current Utilities allowance would more than cover their mortgages and their properties would have increased in value 100%+.
If you were to do the same now, though, you would face a VERY large shortfall on a mortgage of even a modest place. If the property values continue to boom you might do well after a few years. I personally think this would be VERY high risk, as I have been told by numerous people that a correction is on it's way.
The Utilities allowance will not rent you a place even close to the equivelant company accomodation, and the gap between the two would seem to be widening.
My advice would be take company accomodation, as it's a roof over your head whilst you get some local knowledge. It IS a crap-shoot, though people who have been unhappy with their first assignement have been able to negotiate compromises with a bit of persistence.
You can opt out later, but it states very clearly in the contract that you can't opt back in.