Just to be clear, the JAMMA kit spits out 640x480...
So you don't need 1080p at all, in fact the SLG3000 wouldn't work in conjunction with the scaler, if it output anything higher.
The xRGB mini on the other hand, that 100% needs and looks better in 1080p via HDMI vs 1366x768 via DVI.
In my personal observation the new screen looked better in just about ever way.
But remember I didn't do a lag test with the old screen, based on Derick's findings it may actually be slightly lower.
So in some areas, the new screen could be a regression honestly.
I'm open to healthy debate on the subject, the quest for true specs demands it!

I'm also very happy with my setup, thankfully... You know I'd be dumping more coin if I wasn't.
I do think part of the reason why Vewlix Diamond's have this "legendary screen" associated with them...
The manufacture is called "IPS" which leads people to believe its a IPS technology screen.
This is not at all correct of course, its a LCD tech.
P.S. If someday Taito makes an actual IPS tech screen, drop in replacement kit, for the Vewlix OMFG!... *drool*