I guess it depends on what we are talking about. If we are talking about any one speaker in our front soundstage sounding different than the other two it would be a problem, imo. That said, I actually wonder how much difference there is in any of these speakers and if mix-n-matched would there be positive and negative attributes people could pick up without knowing which speaker was which. One thing we can all agree on--dean's crossovers are going to look better than what came out of those RF-7IIs.
I agree... it can matter and does matter to most.
I do recognize that there are timbre differences in every speaker system, and in a lot of instances... vast differences, but my ref center has become "fairly" seamless with my cornwalls with the application of a little creative EQ'ing. It surely was not seamless right out of the box and would never be if I ran my EQ flat.
I have to emphasis the word "Fairly" in relation to seamless... and more so now that Deans work has cleaned up and focused my CW's.