I'd say it's a worthy upgrade. Certainly the best it's ever going to look.
I bought the 4K edition, UK version - last copy left in the shop. The packaging is actually a big downgrade compared to the old US Criterion DVD edition I've got. The DVD has a double gatefold, with the booklet and poster inserted alongside, instead of a single wide insert with the discs stacked on top of each other.
The paper stock in the DVD's booklet is much, much nicer (textured, not glossy) and the 4K one has been cropped at the top and bottom so the text is the same size but the page layout is more cramped. Bizarrely, the 4K copy's poster is slightly larger, but only because it has extra white space around the edge (and is also printed on glossy stock). The DVD's outer cover is thicker and feels more expensive.
You'd think if it's the ultimate edition, they'd treat the packaging with a little more respect. I might just swap the discs over (but the ones in the DVD box are designed to fit with the design on the background).