@tumdum I guess 'it depends' :D - for 'clearly this should have been different in the first place' amending makes sense, but for 'this alternate way of doing things is superior' or 'this additional thing is needed as well' separate commits can be nice.
If the contribution already consists of multiple commits and the change 'belongs' to one of the 'earlier' commits, going back and amending that commit might not be worth it. Might make sense to squash the whole thing though :D