Credit card on my PSN account has expired now, as I rarely have to put anything into my online wallet.
If you're concerned, look into having a new card issued - so long as it's a relatively quick process and you won't go cold turkey without it for a week or two, get in touch with your bank to give yourself some piece of mind.
I'd never really worried until I got hit by online fraud a few years ago - they bought A FUCKING CAR with my card, and the idiotic retailer let them provide card details over the phone. Despite being covered for this sort of thing, it's still an unpleasant experience. Now I have fraud protection to go along with the usual protection a credit card offers - should the PSN hackers manage to do anything with the information that was at risk, it's an extra safety net. My fraud protection service actually got in touch today asking if myself or any of my family had a PSN account.