GoForSmoke:
If you ever do need more power, use a pin through a good bit of resistor to control a transistor that can safely carry the extra. Or use a chip to do the same thing, I've used opto-isolators to control external power use before.
In this situation, where the entire circuit is self-contained, I wouldn't think an optoisolator would be needed. A basic transistor should be fine. I would only use an optoisolator for interfacing between circuits where I wanted to keep the ground potentials separate.