In this market some builders are very motivated to reduce their inventory. I recently negotiated an additional $7000 off of a spec townhome that had been recently reduced $5000. A few weeks ago I found a $487,000 home that was marked down to $387,000... a $100,000 reduction! That house ended up selling in multiple offers.
Since you have already selected a home, it is possible that an agent working on your behalf may not be able to receive a cooperating commission from the builder if you've already have significant intereactions with the builder or its representatives. If that's the case, you would need to negotiate with an agent to provide them direct compensation for representation, but I believe that in almost all circumstances you'll find the agent's ability to negotiate on your behalf to be well worth it.
Just a side note, I say that having represented a builder for over 4 years....
If you'd like more info, I'd be happy to help and represent you, if you'd like! I know the area well, as I lived in Woodbury for 22 years! All my contact info is on my website. http://www.toddnorsted.com
Again, I would surely recommend having a Realtor working on your behalf.