Even if you just buy your own house, the commissions that you would save would more than justify the cost of getting the license.  

I make more renting each br separately in a 2br unit.I offer my cleaner and/or my other unit tenants a commission bonus ($50) for showing the place to someone who signs a lease (docusigned directly with me from afar).

There are conventional 3% loans, but your mortgage broker will have their commissions taken back if you sell prior to 6 months. 

Compare that to a potential $4k/year cf, it would take almost 5 years to get the same money you would if you sold (assuming 15% fees/commissions/closing).If you reinvested the profit from the sale, you should be able to still get the same or better cf in a different property.

Plus once I have my license it will be a lot easier to right up my own offers on the MLS and not inconvenience a real estate agent with a lot of offers and a low commission.

Also, are broker's paying themselves commission if they do purchase/sell a house or are they just deducting it from the purchase price as the commission is taxable?

I'd have people come in with cash to buy/sell at mtgox  +/- 10-15%  (if I had too much cash, I'd lower commission to sell, etc.).   

The agreement between the Seller and Agent may include getting paid the commission upon the sale of the property, regardless of what your offer states.  

Does anyone have any idea why an agent will be uninterested in communicating about a property that would result in pretty big commission check?

These people are brokers who get a commission for a company called sharestates.