My company (
http://www.usablehq.com/) has been through an accelerator (
http://ignite100.com). The money we got was useful, definitely, but that's not why we did it. We could have bootstrapped. The main advantage of an accelerator is that you get to put your ideas in front of a stream of very smart people who each have experience of building companies. You get to learn from their mistakes. That's tremendously useful. In 3 days of the Ignite programme we pitched to about 40 entrepreneurs, and many more during the rest of the 13 weeks. Those people are now amazing contacts, fantastic mentors, and in some cases, investors in subsequent rounds. I genuinely believe Usable wouldn't be in the position it is now without them.
Getting to revenue ASAP is important (in some cases, it depends on the business obviously), but focusing entirely on that will distract you from opportunities that improve what you're offering in the long term. Ultimately, if you're bootstrapping, most of the time you're focussed on cash-flow, and that means you'll miss some important things. Accelerators are a straightforward way around that issue.
Sidenote: The YC thing... YC is amazing because Paul Graham et al are very, very good at picking teams. It's an endorsement from people who really know what they're doing. As the start-up accelerator business grows we'll see similarly trusted recommendations from some of the people choosing teams at other accelerators, and consequently that side of the value will increase. Most accelerators are too new for that to be the case now.