To be honest, I'll be more than happy with a general sharpening of the image quality, especially in the first few seasons, and then redoing/updating any effects that look "off" as a result of the higher resolution. Otherwise leave them be.
If this project definitely goes ahead, they've gone a tonne
of work ahead of them anywa; upgrading the picture quality is going to be really hard I think on some of the earlier seasons especially. The fuzziness is quite noticeable even in SD DVD format. No need to give themselves even more work beyond that.