The Fifth Element was one of the earlier Blu-Rays (2006) and had its share of problems. In 2007 it was released as a Remastered disc which improved on many of those issues.
In 2015, it was released under sony's new "Remastered in 4K" series in 2 different formats: A Blu-Ray only version and a "Supreme Cinema" series which includes a book. Both versions include the SAME disc.. the supreme cinema series only includes a book alongside it.
Owning several versions of The Fifth Element on VHS, DVD, Superbit DVD, UMD, Digital download and all 3 Blu-Rays.. I definitely prefer the current Blu-Ray.
Video-wise, I found it to be a slight upgrade over the earlier blu-rays (it's a bit more vibrant, but other than that it's not too noticeable)
Audio-wise, it now includes a 7.1 Dolby Atmos soundtrack which was amazing (and sounded like an upgrade even on a non-atmos setup compared to the 2011 release)
Extras-wise, it includes all of the features available from the DVD that never made it to blu-ray (on the downside, they're not in HD).
In the end, is it worth it?
I hear the Supreme Cinema book has its issues, but the standalone release comes in a nice slipcover and normal blu-ray case, looks better, sounds better, has a bunch of extras and is definitely affordable.
You won't see the same upgrade as in other titles like Leon (regular blu ray vs. re-release) but for a fan, I'm not disappointed. I find it to be the best version of the film so far.