Hell yes, having security on your CV is a Good Thing. I get more recruiters contacting me because of the background I have in security than for any other reason. And those aren't just for purely security jobs. Some are for sysadminning, some programming, some teaching, even some incident analysis/computer forensics. Even if you later end up in a job where security isn't part of your remit - like I am now - people will sit up and pay attention if you can talk sensibly about intrusion prevention, data and system integrity, authentication, encryption, backups, disaster recovery and their ilk.