Yes and no...
If you change them out, you will notice a nice difference if you go w/ the right set-up / drivers to optimize the 40W peak power they get.
Simply put though... you really don't want anything that will bolt right into the tuned ports. Why? Simple physics. The tuned ports drivers are 5.25". Good luck finding any driver w/ a decent low freq range (let alone one that doesn't require gobs of power) in that size. Instead, you need to move up to 6.5-6.75 or 6x9" drivers and make a baffle to replace the tuned port.
So, change the drivers (all of them) and leave room for expansion later if desired (in amp and head unit). There are lots of DIYs here and the Boxster wiki (including a baffle template). Just do a search and you will find plenty.
Good luck
