I think I've actually figured out the issue, although it doesn't seem right.
the dimensions were in a class that was turned off in my navigation palette, but visible in the viewport. This doesn't make any sense to me - if I'm in a viewport, my navigation settings should be irrelevant? The viewport controls class visibility?
anyways, once I turned the class on, even though it's on... I was able to select similar the dimensions.
Thanks,
Allison