I love my 2007 kentfield, but I'm not the drop bar type. I couldn't imagine spending the money to pay someone to convert it to drop bars considering the amount of parts needed. I'm sure labor might be a little much too. After riding for a while I did notice that I wanted to opportunity to stretch out and not be so upright. I'm still not into drop bars so I wanted somthing in between. I got a pair of rather long bar ends that go straight forward and then curve parallel to the bar. I wrapped them with bar tape and put grips on the ends. this is enough for me and it added about 4 more comfortable hand positions. I can still up shift from the bar ends and do some moderate braking. This works for me.
Unless it has changed the Marin Kentfield goes for around $330. For what you'd spend to have it converted you could buy a different, possibly better bike that might be more of what you want. If you are going to spend the money on a brand new bike (which all of us commuters deserve if we so desire) You shouldn't have to settle. It is an investment you should be happy with, not regret.