Funny, dreadlocks might even impress me if focused intelligence is the first thing that came out of his mouth.
On the flip side, a conventional haircut on someone who appears distracted begins a sentence with umm while rifling through their files is going to lower my confidence.
We have a few seconds to make an impression, both of our knowledge and our focus. The moment you make, or don't make, eye contact and begin to speak is going to set the perception that will stick, positively or negatively. A conventional appearance can increase tolerance of an otherwise imperfect 1st impression so it isn't a bad idea for someone starting out and still working on their routine.