I remember last year when I had a gig with a band that only occasionally gigged. We basically played the same venue every 3 months - a wine bar that was populated by drunk people looking for a late drink. I got to the point where I got in from work and couldn't be arsed to get ready for the gig. The other band members were feeling the same. Yet I recall when I was a young lad, every gig would have me excited for at least a week before.
It's all about familiarity. Generally, if you're a pro musician, you'll eventually treat gigging the same as any day job. It seems great, but you're actually putting in more hours than a regular job, what with the travelling, setting up, etc.
Also, I tend to find that if you think a gig is going to be great, it generally turns out crap. But then vice versa.