just go for the whole thing, i upgraded part by part in one of my older cars, including adding components to a non component car and it was fantastic, just the head unit alone brought out better quality from the stock speakers. then i got some new fronts, got better, then i got new rears, even better, went component up front, continued to get better, added and amp to the speakers and some subs and an amp, it was 1000% increase in every way shape and form.
Now i have a base with sport with the non bose system. i have a whole pile of stuff just waiting to go in, it can all be found here:
Lots of toys showing up lately....
I love having a system. the bose is nice but i miss having a complete audio system thats properly powered. Nothing beats crystal clarity and a nice boom !