As the Tech Assistant at a public high school, there's nothing wrong with my dual core from 2010. I've bumped the RAM to 8GB, and have more local storage than our SAN, thanks to spare parts that wind up in my case instead of a drawer.
For travel, I've got a netbook like the students, but mine is a little special. One of the MBs failed, and the warranty replacement included a nicer CPU/Board.
We used to have a replacement cycle, but that budget went to the netbooks, so desktops get internal upgrades.
As a side note, how do you feel about Windows Experience Scores? They're not perfect, but they offer a comparison you can do on every Windows machine. I look at individual scores, not the 3.2 they get for having integrated graphics.