This won't be an issue in the new building for people on WiFi (I'll be setting it up with WPA2). But wouldn't people on the wired LAN be vulnerable to this until these services start finally using https?
I am amazed the whole thing survives.
I am in a not so much larger environment in terms of user number, and we have € 40,000 (or more) worth Cisco network equipment, and a 20 Mbps fiber optics data link.
Compared to your setup, it may look great, and still, without some serious bandwidth shaping, we would be in trouble daily in peak hours: bandwidth maxed out, p2p, and what not.
We do have some Graduate School population, here, which seems on average significantly more sensible than 20 year old kids, but still...
You do need better equipment and a redesigned network. And, I suggest you only give wireless access to residential areas, if possible That may save you some problems.