Domain logon performance over leased line.

I have a domain controller hosting total of 55 users on a
windows server.
10 of these users connect to my Citrix terminal server via
64k fixed line. Now these 10 users do not log on to the
domain when they switch on their pc's every morning. They
simply have a workgroup on their side.

These 10 users run WinXP Pro with full admin rights. They
are pretty well diciplined and don't abuse that right.

I did it this way thinking I might conserve more precious
bandwidth.
It is working quite well for us, but I'm wondering how
much method there is in my madness? Will bandwidth really
suffer if they log on to the domain?...keeping in mind
that active directory runs on the domain controller.

I might even decide to deploy group policies from our
Windows 2003 Server at a later stage.

Some advice/comments/suggestions will be much appreciated
here.

Thanks