I wouldn't use an external amplifier on them if those are the only speakers you plan on using. Not worth the monetary investment.
However, if you are going to upgrade speakers in the near future to something from the aftermarket, there is nothing inherently wrong with amplifying stock speakers in the short term. Hell, I used an amp w/ my stock tweeters for a while //content.invisioncic.com/y282845/emoticons/tongue.gif.6130eb82179565f6db8d26d6001dcd24.gif