I did matching stuff when my big girls were smaller and they always looked lovely. Now I do sometime buy them the same thing or the same thing in different colours or patterns if it's something they will like but obviously they don't wear them at the same time - except by accident YANBU in my view.
dressing them the same, or with identical very bright items (rainbow swimsuits, very PINK hats) can be really useful when you're looking for one in a crowd. 'Have you seen one like this >>>> but bigger / smaller?' works really well
worked best when we dyed dd1 and dd2's hair pink one summer
if you do the identical snuggly pjs thing please make sure you take photos