I think it depends on how aggressive you want and how you use your car! There might be some performance gains you might feel with your butt dyno, but it's mainly going to be aural.
This is the sound clip of the full system:
http://www.2addicts.com/forums/showthread.php?t=1409564
This has soundclips of just the midpipe replaced with Dinan's:
http://www.2addicts.com/forums/showthread.php?t=1399984
Personally, I'm sticking with just the midpipe because the full Dinan exhaust deletes the valved system. My car is a daily driver so I want to retain the cruising mode vs. sport mode. If I want to be really loud, I hop in my open header V8 car.
Alternatively, you could do MPE and the midpipe to keep the valve, but it looks like it's a little extra work to get them to mate up.