I just upgraded from C1-6 to C1-1.1.3, I'd back up Kevin's comments actually. The sharpening alone on our Aptus II-8 is the equivalent of around 8 more megapixels, Guy Flesher over on GetDPI says 10. I'm going back and upgrading some 800 books (150K files) shot in our repro studio with the older software to the new engine, a lot of work but the difference really is that significant.
In general it is often the case that significant steps ahead in a raw processing engine can make an older camera into a new 'being', give it newer life. This was the case with ACR when they changed over to the 2010 engine and I assume again when they went ahead with the 2012 engine (though I don't like so don't use it). Case in point, Canon 1Ds original. I always found the files incredibly difficult to work with, especially higher ISO. That was back with whatever ACR was current when I owned the camera in 2005. Using process 2010 it's a different world, I managed to rescue certain difficult to process shots from a trip to Iceland, 7 years later, it really was a new camera. Here is one.
(http://www.getdpi.com/gallery/files/8/9/8/krafla2.jpg)
But don't take anyone's word for it, honestly, download C1-7.1.3 and try it out for yourself, do the comparisons.