I wouldn't worry too much. I went to one last summer and jeans are fine, it's a fairly informal event. It's an open day, so you're the (potential) customer at the end of the day- it's their job to impress you rather than the other way round.
It looked to me as Joe Public like a great facility and I learnt a lot about the courses, but not as much qualitative information about employment after training. I for one enjoyed the day and came away feeling positive, talked out of going to university and ready to take the plunge. In fact I think I've actually got an application in their system which I started on the day for the promise of a £20 discount.
Since then I've made a firm decision not to go integrated, but going home that day I was completely sold, as were my parents. I had a Cabair seminar in my diary as well, and I think I could have just as easily been impressed by them, borrowed the £70k against our house and lost everything.