Very nice upgrade. I'm sure you'll enjoy it.
One thought: The Polks, although a fine speaker, may be the weakest link in your system. My thinking on home and auto audio is that the speakers should constitute roughly 50% of your budget. But, you have apparently done your homework and I'm sure you picked the speakers for good reasons. They're actually what I went for for my 1st upgrade, and ended up upgrading them, heh.
NCC1701, I completely agree with your point on the Polks. In fact the only reason they are my speakers of choice is because they are already installed in the car.
What happened was that I bought my Smart back in February and the factory speakers really weren't cutting it. Having an audio system that's at least decent really matters to me. That being said, I purchased the pair of polks DB651 for a quick upgrade until I decided whether to do a whole system upgrade.
I installed the polks myself (quick job after the door panels are removed) and now that I'll be adding the new HU, sub and amp I'll be keeping them to see the end result.
Ideally I'll be happy enough for now, but the goal is to get a good pair of components to better match the potential of the rest of the system. I'm a bit hesitant as to where would be the best place for the tweets when going down the component route, as I like to keep the factory look in the car - but that's a problem for later.
Thanks for you thoughts on my upgrade. Hoping to do it next weekend as some of the parts won't get to me until Monday.