As many others have said, I would definitely recommend implementing some sort of minimum requirements for people to be a member of the team.
Try to work with what you have. Maybe work with some of the students who are into spirit and have them transition into a PR/awards role. We have had some of our more creative members make a team yearbook/portfolio to show the judges. It was filled with useful information about our team and it also looked fantastic. Perhaps you have someone interested in drawing who you might be able to get involved in the design process. Remember that there is also animation, web design, and other tasks for the more creative/artistic students on the team. Don't dismiss them simply because they can't/don't want to actually build the robot.
When 25 travels to other regionals outside of New Jersey, a list of all the responsibilities is made and then the list is populated with members to fill them. This helps to make sure that everyone is there with a purpose.
I would also recommend checking out
this recent thread about team attitude. Some of the posts in there might be useful to you.
As you move forward, remember that spirit isn't all bad. You just need to find the right balance. You don't want to make FIRST unfun for those students who really want to be a part of it.
To add to my post: I was in a similar position to you a few years back. A bunch of new students joined the team and wanted to focus entirely on the team image, including spirit. I was incredibly resistant to this initially. I was a programmer and PR person and nearly all my time at competitions was spent in the pits. What happened in the stands outside of scouting was unimportant to me. I didn't understand why we needed people to focus on making the team look good. I thought it was a waste.
In the end, I let them do as they pleased. And you know what? I
love where the team is now. I feel as if we have become more complete now that we embrace some of the things we used to dismiss.