g729 is a CPU killer. There are cards you can install to offload the g729 processing, but we don't have any experience with them. If you can stop using g729, you should see the load decrease dramatically.
You could look at adding more servers to your Vicidial to make a cluster.
Vicidial clustering is best done with Vicibox instead of Goautodial, but it's still possible on goautodial just not as easy. Look for the Vicidial Multi-Server Manual. We wrote it, and it was written back when the version of Vicidial you are presently using was "The Latest". LOL
Also worthy of note: If you are using AMD or Survey campaigns, you can also add a lot of load to the server pretty quickly, since you said your calls are inbound that should not be the case, but I thought I'd mention it.