I have to agree with Jim on the fuel mileage as I have a 28' cargo deck trailer (32' from center of ball to back of trailer) and yes it seems huge when the 7 is inside of it but it also has enough room to haul anything else you might wish to transport such as a tool chest and jack and stands or spare tire sets either in front or behind the car. I also tow it with an F-350 Super Duty Crew Cab Diesel that averages 14 to 15 MPG with the trailer in tow depending if I am running 65 MPH or just a little faster depending on traffic conditions. My normal average MPG without the trailer running 65 MPH with the cruse set is 18.5 MPG and 14.7 in town traffic. By the way I do not suggest that you use the cruse control when towing for safety reasons but that is just my belief and also what the manufacture of my tow vehicle recommends when towing.
The draw backs that I see with a 16' trailer are these; only a seven or a Miata or similar wheel base car will fit, little to no storage room on the deck for other items such as a tool chest unless small, cost is not much less than a 24' to 28' enclosed trailer due to the fewer number of car hauler trailers made in that size from what I have seen that are available, payload is usually lower than the 24' to 28' trailers. Plus's for the smaller trailer; can be stored inside most 24' long garages, easier to control when backing up to a point (factor of tongue length and overall length), less expensive to register in some states due to length.
One thing to consider is the tow vehicle ability to properly stop the trailer when loaded and the max tongue weight of the tow vehicle with or with out trailer brakes as that is where most folks get into trouble when towing a trailer as the tow vehicle is either maxed out or is just to small for the trailer and not able to safely stop a trailer larger than a small utility trailer in an emergency situation.
Also consider a sway control and load leveler hitch as they seem to pay for them selves if your doing any long tows or traveling on the freeways but that is just my belief.
Here is a link to the setup I have: http://usa7s.com/vb/showthread.php?t=4360&page=2 Post # 18
Hope this helps.