The best way to get into YC is to build a great business :)
pg wrote about this pretty convincingly here: http://paulgraham.com/equity.html
Unless you are comparing YC against an actual term sheet in your hand with at least 2X better terms, that YC is overwhelmingly likely a good deal. There might be good reasons not to enter YC for some companies, but the 6% equity is rarely the determining one, even for companies with revenue and sustainable Ramen profits.
It sounds like everybody that participates says they make more progress in the program than they would have otherwise in that amount of time.
But if you have a successful business then you probably don't NEED them. But they can still help.