It depends for me, I would never run mismatched tires period, mismatched wheels don't bother me as much if they are the same color ans shape. I recently added LX cantilevers to an MTB restore while the existing are dia-compe 987s, finding used 987s for a decent price kept me from matching them.
I do try my best with my vintage camp road bikes to keep them as close to full groupos but money is a factor