"Specializing" in a certain type of practice in optometry is practically nonexistent in legal terms. Optometrists are legally not allowed to claim that they are a "Contact Lens Specialist," etc. after doing a CL residency because there is no board certification process, like where surgeons obtain an FACS attached to their name (e.g. Dr. Bob Brown MD, FACS). To clarify, board certification process = more board exams.
Dr. Gump, IMHO I think that "specializing" through a residency could (and not necessarily will) help your bottom line. For example, a Visual Therapy practice on the side could bring in a different pool of patients (kids, stroke survivors with ocular issues, etc.). Also a general practice residency will enhance your optometric education and thus make you a better clinician. I know I'm speaking in general terms but we can all agree that better patient care could easily make you stand out in the public beyond all the other optometrists in town.
I also wanted to add that true, legal specialties could be a detriment to our profession. If optometry introduced board certification, the docs that don't have this certification will be screwed over because all these new board certified docs can legally claim their specialty and thus make the older docs look bad. That means all the older docs are forced to do something to become board certified, and I'm sure that would anger them.
So you have to ask, attaching "Board Certified in Contact Lenses" to your business card sounds really cool, but is specialization truly better for the patient?