I've been upgraded to BE eight times in the last month going in and out of Guatemala City -- it must be a very low elite traveled route. Previous poster is correct -- it's just domestic F, not BE. That said, both ways you get a quiet cabin, comfortable seats, a nice lunch, and usually good service and quick drink refills.
The Guatemala City airport is much improved from just a few years ago. Bags arrive quickly, immigration line moves quickly and efficiently, and customs usually consists of being waved through. Even the exit area which used to be mob scene is much better now.
When you leave, the Delta priority line usually has no one waiting and you breeze right through check-in. There is no executive lounge of any type that I know of, but several of the restaurants (once through security) have free internet if you buy something, even a cup of coffee and a pastry.