Dambus,
This property was rather nice, probably the nicest hotel on the island. It is not very far from the airport actually, no more than a 10min drive/ride. I don't remember how much we paid for the taxi, but it wasn't unreasonable. Less than $20US. And it is also less than 10min to the center of Willemstad.
The hotel rooms, while very clean, are in need of renovation. The common areas and restaurants are modern and nicely decorated/furnished, but the rooms are due for a refurbishment. I suspect that will be happening in the not-too-distant future as Marriott has recently taken over the property from Sonesta Hotels.
As for upgrades, the best advice I can offer is to ask for a room fronting the Caribbean Sea, as there are not many of them and I assume those are considered upgrades. Pleased with the overall experience at the Curacao Marriott!
Hope you enjoy your stay as much as we did, in general. I would like to return to Curacao someday.
AtlMan