There's a few fixes and stuff and some might like the audio flexibility.
The launch screen isn't so bad, at least it gives ready access to a number of files new players might want to access. It might have nice to have included a mod launching option.
That's all well and good to know, but no one has still answered my question: What the heck is SEIV Deluxe? Can I live without it if I just have SEIVG 1.91-1.94?