Yep. There is no way to have AI racers against you. A shame, but it is a game meant for online racing (in fact it begun as a little amusement for the author and his friends and in some way that is what it continues to be).
The lack of active races right now is because of the day hour it is. The game is spanish, so it is at european afternoon time when the people connects to play (ca. 20pm-2am GMT+1). There seems to be also a community of brazilians which use to play (they must be at GMT-4 or something like that), so the only race you've seen is the one from some noctamboulus brazilians (lol). When I used the play there used to be also a couple of brits, germans and frenchies. At european afternoon time there are races with a lot of people and they usually are A LOT funny, especially when the race host has activated the collisions. Imagine that you are meters away from the pole in your qualifying lap and then a slower guy makes a bad move when you are passing near him so it messes your lap. I remember a lot of arguments in the chat of the game because of this. Very fun :D.
As for the problems on connect check if you have an active firewall which is blocking access to Internet to MRO. If this is what happens, open port TCP 6666 for it (this is the port it uses) and if the race is active and has free access you should have no problems to enter. It can also happen that the race has ceased to exist and the server is still listing it, but such a situation doesn't use last for a long time, as the server re-scans the races' state quite often.
I've been playing and they've changed the physics. All my deep wisdom for setups has gone and I'm now nowhere near my best times. I'll check the forums for tips on the new physics. They used to be quite simple.
Regards