I have always thought it was a good idea.

I've played the KBS Tour shafts in my last 3 sets of irons, and have always found it useful to blend the shafts across the irons into the wedges.
I'm no expert, but what i've found works for me is to play the Gap wedge at the same spec as my iron set, then soften it for the SW and LW.
So for me, this means I have KBS Tour S flex hard stepped through my irons and 50°, then my 54° and 60° are stand fit shafts because i play a lot less 'full' shots with them.
I've tried shafts like the 'Hi-Rev', and just didn't work for me. But we're all different, and there's substitute for good advice from a knowledgeable fitter.

I play the KBS C-Tapers in my irons, and got the KBS Hi-Rev in my wedges.

I think they are a great complement to them. KBS makes great performing shafts.