5
Upgrades help to protect your web site from vulnerabilities.
There are groups out there that compete to see who is the best at taking down websites, and who can take down the most websites per day. They look for vulnerabilities through modules, php, etc.... Recently the Adsense module had a security hole, they simply google/search for that module and start taking sites down. Zone H
http://www.zone-h.org/ keeps records, one group was taking down 1000 websites a day.
It may be a pain to upgrade, but it's part of what you need to do to maintain your website. If you don't maintain it and keep it up to date, you'll lose it.
Even this site has been taken down a couple of times.
