How Dedicated Must a Dedicated Circuit Be?

I am moving into a house that has a room with two circuits which just service that room. Each circuit feeds a string of outlets and ends at a ceiling lamp. There are no refrigerators, computers, motors or other nasties on each circuit - just one or two light bulbs at the end of the line. They are both 15A. I am planning on adding a 20A circuit for the amps and maybe using one of each for digital and non-digital sources.

My Questions:

1) Does the existance of a lightbulb at the end of a circuit make it a lesser "dedicated circuit"?

2) If it qualifies as a decent dedicated circuit, wouldn't it be true that many of us already have dedicated circuits that are just outlet loops with no other "nasties" plugged into them?

Thanks. I'll take my answer off the air. Peter