I'm not a fan of aftermarket audio. I simply don't like the look of a non-factory deck and/or amps/subwoofers in the back, and on top of that...I'm not much of an audiophile. That said, simply replacing the speakers like you have done would likely be the route I'd go if I ever get around to it.
bigaudiofanat, would you say that just replacing the 4 speakers and nothing else in a Base would be a worthwhile upgrade, or is it one of those things where if you're not going to do it right, don't do it all? I would also do this only if I didn't have to cut trim for provisions for larger speakers or alter the look of the interior in any way...just plug-n-play replacements.
From my limited knowledge of car-audio, I understand that it's often the factory head-unit (and their built-in amps) which leave the biggest room for improvement, so would replacement speakers powered by a factory deck make a noticeable difference?