18 days is not much time considering a special order. When we went to the dealer when looking to order our Acadia.. they told us the average wait was 6-8 weeks. But we ended up finding an Acadia locally that is almost exactly how we would have ordered it minus one option... I wanted the 110v outlet.. but I can always add an inverter.
I was facing the same dilema when shopping for my Outlook. Endend up with fully loaded model which was available on the lot. There were couple of extras I wasn't particularly interested in (like the towing package, the rear seat dvd or the expensive paint option), but I chose to go with that one instead of waiting for an ordered one (which on practice had to be 2009 as dealer told me at the time 2008's can't be ordered anymore (2 weeks ago from now). I was facing the choice of waiting for my car until end of August/begining of September, unsure about pricing (2009 model), or getting this one off the lot and driving away, and more importantly - have the car for the summer - with the new oncoming family member (who BTW was born yesterday ) this was quite important!
I know what waiting for a car means (personal experience from my diesel Passat back in 2004) - I feel your pain. Hopefully wait won't be much longer!