Why not?
If you are going to be there and don't mind paying the ticket price (or qualify for a free one), then do it. I paid to go to opening reception of the US Chess Championships one year and had I been free during the event I might have purchased a one-day pass for the event as well. It would be interesting to do at least once, in my opinion, unless you are able to go to events frequented by well known GMs more easily some other way.
Hi
I'm passing through London during the London chess classic and have thought about gong to watch in person one of the days / nights. I've never been to watch a tournament. Is it something worth doing?