i would say that the main advantage of optometry over many other allied health professions, is that optometry is funded fairly well under the national medicare system. you can visit an optometrist without a doctor's referral.
Patients of other allied health professions such as physiotherapy, chiro, podiatrist, etc etc may be entitled to 5 sessions per year with the doctor's referral under Medicare's EPC (ehanced primary care)
basically, if you open up a clinic, its relatively easier to get patients and build your numbers up quicker than other professions. secondly, you can sell glasses and make a nice income stream from that. if you're dodgy, you can sell sunnies via health fund rebates too.(not recommended)
cons: due to equipment costs, it would be more expensive to open up initially, compared to a GP surgery, physio clinic, podiatrists clinic...
its fairly easy to see that in expensive rental areas such as westfileds, you will see numerous optometrists because they can afford that sort of rent. if you see doctors in shopping centres, they're usually hidden away in some corner where the rents are cheaper.