Didn't you know, everyone here already owns 10+ DVD Burners and just adds more drives for no reason?
Actually, if you're still getting good burns and no problems with your discs, then that's pretty much the best way of deciding. You may want to consider a new drive though if your current one is 4x or slower, or 8x and doesn't have very good firmware support for newer 16x media. Some 8x burners do fine with most 16x media with their latest firmware, but some 8x burners are bad even with a lot of 8x media and have terrible support for 16x media. In any event, updating your drive's firmware to the latest and/or best is always a good idea.