I just got a wind deflector for the X. I went back and forth about getting one, untill i came across a used one on Craigslist that i picked up for $75, brand new there around $400!
I went from 6.5-7 mpg towing my trailer to 8.5! Yes i gained that mich with the deflector. My trailer is 11.5 feet tall. So anything that can get the air up over the trailer instead of slamming into the front is helpful.
BTW, towing at 55 will get better mileage than towing at 75 (i've witnessed that many times). With every increase in mph there is also a decrease in mpg. At 55 on back roads i used to get near 9. I normally travel at 62-67 mph.