The only problem that I see with running straight DC for your lighting is the size of the wires you need to run 12 volts any distance without power loss. Converting it to 120 volts AC allows you to use reasonable sized wire and run your wires further without line losses. AC also doesn't arc in a switch the way DC does when you turn on a circuit with a load. Of course, that's not a problem when the load is a couple of LED lights, they don't draw much power.