Am I being a pain by "collecting" library cards?

I live in California where any resident can get a card for any public library. So when I go to a new city or county, I try to visit the local library and sign up for a card. I never check anything out, but I like to keep the card in my collection. I have about 30 so far.

Am I being a pain here? Wasting the staff's time? Costing them any extra money? On the flip side, am I helping their stats in any way?