When we went- it wasn't what I expected. It was in Richmond, and we were stuck in a basement room and watched the ceremony upstairs in a grandball room via closed circuit TV. BECAUSE HE WAS IN MIKE CO at that point- going through IFS.
Of course, we were able to go up for the 'fun' part, but there were so many people, it was kind of ridiculous. Plus many of his Charlie '06 Co. had moved on to their MOS schools.
We didn't get a hotel room, so we carpooled (and had a DD) back to Stafford. I think the cost of the Ball alone was $75 per person.
That's just one of my experiences. I WOULD recommend going, since it is a special occasion.

And everyone's experience is different. Plus your GF would probably want to get dressed up and meet some of your fellow TBS buddies.