Is a higher credit limit worth it?

Last week's news about credit card security breaches at Winners and CIBC made for some interesting discussion over brunch with friends of mine on Sunday morning.

Since giving me my first student credit card with a $500 monthly limit about 7 years ago, I noticed as Visa dutifully and repeatedly kept upping my credit limit, without my asking, for no other reason than I had the audacity to pay my bill on time. It's gotten so out of hand that my credit limit on the card currently stands at $12,000 -- a figure that's amazing enough in its own right but all the more so considering it represents about 25% of my annual income.

I never really thought much about it (beyond some small part of me vainly thinking it was some sort of status symbol) but recent events have me worried it might be more trouble than its worth.

I've recently been trying to spend as much as possible on my credit card, for two main reasons. I'm trying to maximize my reward points (with the security of knowing I won't get into any serious debt since I pay the balance every month) and I'm also hoping to create enough of a credit history that I can get a mortgage at as good a rate as posiible in a few years. I don’t really know how nebulous things like credit scores are calculated -- the indsutry appears to thrive on secrecy -- but I generally assumed that the more debt I accumulated, and the faster I paid it off, the better I'd look to lenders.

Whatever advantages there are to having a better credit score, I'm guessing they're more than negated by having illegal charges show up on your credit card bill. The TJX and CIBC stories have me thinking, if it's this easy to get access to sensitive information like my bank account numbers, it won't be too long until I start seeing things I didn't pay for show up in my Visa account. And $10,000 worth of unused credit space every month can certainly make room for some serious purchases. I'm relatively confident that I wouldn't be paying out of pocket for any of these purchases myself, since Visa seems to accept the liability for fraudulent activity, but there's always the chance. And it's enough to have me worried.

I'm tempted to get RBC to bring my credit limit down to a more manageable level, something in the neighbourhood of $2000 a month. My question to the blogosphere is whether or not that might have any detrimental effect on my credit score.