I did that on my old race server, and it kind of sucked. One problem is that the bots know nothing about the zones, so you can't play against them at all. No playing against bots means that it'll be rare that someone stays long enough for a second person to join, which means the server will rarely fill up.
Also it's impossible to find an expansion speed so that it's playable for newbies who can't go that fast while still being a real threat for experienced players.