Consider your motivations
Saba Karim (Techstars) had some really interesting insight into joining an accelerator. More precisely, why you shouldn't join an accelerator.
It's all about what you want to get out of the experience. Motivation is everything, it seems.
TL;DR - Don't join an accelerator if:
You only want to get funding - but if you need more, then maybe?
To do customer development - you don't need an accelerator to validate your product or idea with customers.
To get a list of investors - you can get this cheaper and more easily from other sources like Crunchbase.
You need motivation - we are all adults here. If you aren't internally motivated, an accelerator won't provide it.
To get a merit badge - Once you are successful, nobody really cares if you went to "XYZ Accelerator." The only 'merit badge' you want is success!
Somebody said you should - Everybody's got an opinion, but the only ones that matter are yours and your customer's opinions.
Something to think about.