Yet another car stereo question

I know that many threads have been posted about upgrades to the Boxster stereo system but I have a few questions.

I currently have front dash only speakers and a CDR23 with no amplifier. It sounds a little better than a walkie-talkie. There has been much said about the Boxster being a noisy car and that a premium sound system is a waste of money. I have also read that the factory front dash speakers are unique in the way they are mounted and that only a limited number of replacements will work (like the Dynaudio or MBQuart)

My questions are:

1. Would getting an amp only improve the sound of my current set up? If so which one?
2. Would getting a new radio with built in amp be a better idea? Any recommendations that would visually fit the interior with out looking too ghetto?
3. Would just getting new dash speakers improve the CDR23?
4. Which of the above three would give me the best improvement in sound quality