Hey Jftwp,
Multisite options are best explained here
http://blogs.vmware.com/vsphere/2013/02/vcenter-single-sign-on-part-2-deployment-options.html
Having set that, I would have to agree that the complex the set up is, the more issues if something actually goes down.
In terms of deployment, as SRM is already present for a DR scenerio, the best option would be to go in for a basic/simple primary and DR option.
For removing the single point of failure - SSO, SRM can be used in tandem, as the manual SSO backup process limitations (no clone, block level backup restore tending to break SSO, manually restoring backed up SSO config etc "http://kb.vmware.com/kb/2034928") can be counter intuitive.
In your scenerio, even if you have SSO HA Multisite, the next single point of failure would again be the VC machine itself, and that, with added complexity of an HA multisite setup.
Let me know your thoughts
Regards
a