For me, the corporate events have no social upside, and the career upside is more about making sure to avoid a downside. That is, there's rarely (for my company) a direct networking effect at the actual event ("Hey, Trede, love the outfit, by the way, I've got this opportunity opening up in my department..."). However, people notice who was there and who wasn't, and that can be morphed into who's "on the team" vs. not. Corporate family spirit and all that. If you are looking to get promoted, being seen as "on the team" is a good thing, as management may look to promote the more committed or those who are fitting in.
What to do really depends on what your company's culture is like and what your goals are.