My system is the Bose w/optional rear deck mounted sub. I replaced my stock head unit that crapped out with a JVC HD radio unit, $180 delivered from Crutchfield, and a pair of Focal coaxials in the dash, about $200/
pr. HD radio is great and the dash speakers made a big improvement. Both were very easy to install. Altogether great bang for the buck, IMO.
I also bought a pair of Focals for the doors, which would have required surgery to install. There's no shortage of bass with the sub, so I'm thinking all this effort putting bigger woofers into the doors would be a waste of time and money. If you can find a way to add a factory sub for a $200-$300, that's worthwhile, although without it the system's not too bad.
One word of caution on the dash speakers. Keep the depth to absolutely no more than 55mm or you'll have trouble getting the grills to fit, like I did with the Focal 100CVXs. The 100CA1 coaxials at 53mm deep will fit and are about $60-$70 less.