> I seem to have read somewhere that a 500 status in horizon may be caused by one of the others components failing. So I'm assuming this could be my problem.

Please, run 

# rpm -qa | grep python-django 

[root@openstack ~(keystone_admin)]# rpm -qa | grep python-django 

python-django-appconf-0.6-1.fc19.noarch

python-django-1.5.4-1.fc19.noarch

python-django-openstack-auth-1.1.2-1.fc21.noarch

python-django-compressor-1.3-1.fc19.noarch

python-django-horizon-2013.2-1.fc20.noarch