Upscale the original VFX elements and put them on HD Enterprise?
I think we need to get used to upscaled CGI if we are going to get Voyager and DS9 on Blu. We are already getting upscaled stuff on the Enterprise blu-rays.
In TNG, they've been recreating all the CGI effects from scratch. The Crystalline entity is an example of that.
No one bothered to redo Enterprise's effects because they were mastered in 720p, and deemed "good enough" for Blu-ray. The original CGI for TNG, DS9 and Voyager exists only on the SD tape masters, and all need to be redone for HD.