I've seen lots of people complaining about a time out problem with vpnc. This happens to me even if I'm ping-ing like crazy or not, so its nothing to do with activity on the connection (I think).
The problem with automatically re-connecting was the need to interactively type a password at prompt. Note that this was not my "Xauth password". For some reason my organisation requires an extra password (there are many ways a VPN can be configured).
If you just need to type one username and password, its probable that you can set up your config file to contain:
Xauth username meUserName
Xauth password meSekretPassword
With the above you could just automatically restart vpnc every time it drops out (i.e. using bash). I have this extra password to deal with though, so its a bit harder. Here is the solution achieved using Perl, Expect , and a lot of help from the friendly mst in irc://irc.freenode.net/#Perl