What version of mint(cat /etc/lsb-release)?
What desktop environment are you using?
What drivers are you using?
What kind of display configuration do you want: multimonitor, xinerama, rotation etc.?
For advance I think your problem is that you are using nvidia binary driver from the mint repos, which are too old to support randr1.2 thus the error message(randr1.2 support came from driver version 302.x).
Here's the information you requested:
Version of Mint: Mint 13 Maya
DIsplay Configuration: Xinerama
My goal is two fold, one to have the attached monitor be primary and secondly, if possible, to close the lid on the laptop w/o turning off the attached display.
That does not really sound that you would need xinerama. Closing lid with laptop usually means that laptop will go to sleep, that is usually controlled by DE's power manager settings. Turning panel off is possible with xrandr.
I presume that you are trying to change display properties from mate's own display settings, it is just only gui for command xrandr which might not have all its capabilities. If you are confidient enough yourself, you could try xrandr: http://wiki.debian.org/XStrikeForce/HowToRandR12
But if you are using nvidia binary driver I recommend you to use nvidia-settings, it has nice monitor configuration page that will work without xrandr. If you are unsure which driver do you use, please check what module are loaded with command lsmod(It list all modules that kernel has loaded). If one of them is nvidia, you are using binary driver, if not you are using open source driver(i.e. then there should be module nouveau or vesa or etc.).