IMO there was a noticeable difference with the Core remaster. I felt the instruments in the original sounded kind of muddy, and the remaster sounds much clearer and a little louder.
I think with Purple there just wasn't much to fix. Brendan's production was fairly minimalist, the songs were mostly tracked live with only occasional overdubs, and the resulting album sounded fairly clear and natural.
It doesn't really matter too much to me anyway. I had no problems with the original master, and the main reason I'm buying this is for the additional material.