Hello Curious, you should take the agent you have been working with on your visits to new developments, or if possible, take several of their business cards with you. Your agent will add value to the sales process, and the sales office working with you will also be keeping your agent in the loop as time goes on. As for the various sales offices offering incentives for you because you're not using an outside agent, that's simply not true (here's the caveat) - with offices that claim they are co-operating with the agent you've been working with. They generally offer the very same incentives that they offer everyone else. Your personal agent, however, should be in the "know" of what incentives are being offered throughout the entire development community and would be able to make sure you know about them as well. With that, you and your agent can then begin to ask and negotiate with the developers for terms that would be beneficial. Remember, though, that you have to do this BEFORE you write a contract for purchase, or before you reserve a unit for purchase.
The information you've got from Kevin, Tanja and Michael are valid. You've selected an agent, and may have been working with them, take them with you on your tour of the new developments!
Happy hunting and good luck!