If you are editing video the quad core Macs are the better choice. As for Intel graphics, for normal use - i.e. watching movies, streaming video, playing typical, non-demanding games, they are excellent. Highly GPU-intensive games get decent marks. There has to be some more reviews of using FCP on a HD4000 graphics out there, but I do not have personal experience to recommend one over the other. If in doubt, the video card is always a better choice, even if it means buying a used or refurbed 2011 mini or iMac instead.
P.S., the 2012 mini's are HD4000 only, there isn't any version with a dedicated GPU. So if you want a mini, the 2011 base and mid range models are your best choices. If you do get a 2012 mini (or any Mac with HD4000 graphics), max out the RAM. The Mac will assign more dedicated RAM to the GPU with maxed out RAM.
Here is another thread on your question but not many replies yet (it's recent):
http://forums.creativecow.net/thread/8/1170669