Yep, you are closing the throttle. Happens to everyone. Try just doing what you are doing, not riding them out, untill you are comfortable with how fast the bike comes up. When it doesnt scare you, keeping the throttle open is much easier.
Oh yeah, REMEMBER THE REAR BRAKE. Say "Rear brake" 3 times to your self before bringing it up
Basically, the better you get with the clutch the less revs you will need to bring it up. The higher you bring it up, the less you will have to accelerate to keep it up.
You arent really hurting your clutch. You are putting wear on it, but not like you would be launching it at a drag strip. Even if you wear it out, its just new plates. You are probly huring you chain more than the clutch.
Have fun. Be carefull. REAR BRAKE. And wear your gear.