I have a 12 person office about 4000 miles away (in the EU) from our main office (US). Currently, we have a site to site VPN (10meg, about 80ms latency) which the remote users use for AD and Exchange. They have a few local servers, so file read/write latency isn't an issue. Exchange is also fine. Everything works fine, so I have been working under "If its not broken, don't fix it"
I just wanted a sanity check to see if setting up a new site and putting a DC in that location would buy me anything. Additionally, if done, how would that impact the Exchange server (single instance, 2010, one Mailbox server and one CAS/Hub server). We are also setting up another 2-3 person remote office in the US which I am initially going to continue to support as we do for remote workers (VPN Client connections all day).
The total organization size is small (<100 users), so I don't want to build unnecessary infrastructure, (read: I have a microscopic budget) but I also want to do it right.