well, you also have to consider the team would probably be worth more in a "better" city.
With that said, I believe the NFL could possibly be a "risky" investment at this point. It seems the whole thing is getting saturated. Last season it seemed there was some issues in a lot of places attendance-wise and not the perpetually sold-out image the NFL likes to portray. Then you have the walls caving in on them with all the head trauma stuff, alumni stuff, frivolous fan lawsuits, etc. NCAA Football is also about to enter a real gut check when it comes to the players vs institutions battle. I also believe youth and high school participation is down and will likely go down more, especially when schools/organizations shut it down to avoid lawsuits.
We may be at or close to the height of NFL Football