I recently added a pair of Elac 4pi's and wow.
Like many have said above, re sound stage opening up, tighter bass, much more recognizable detail in all frequencies. I would not want to take them out and actually added a second pair to an office system. I really do feel the super tweeters just upgraded my main floor standers to punch way above their weight and sound like 5x their cost. They weren't cheap but they did add their value and more, imo.