But since I am converting from an xvid - and there is already some quality loss from the DVD to xvid conversion would there really be a noticeable difference visually if I burn all 4 hours to DVD
Yes!..How much "noticeable difference" depends on the tools/methods/settings, used..Only you can SEE what is acceptable for your eyes..
As GIA stated, best to start from original DVD source(s)..Or don't convert at all and (as an alternative) purchase a DVD/Xvid/divx AVI certified player..
Oh yes, I should mention I intend to use ConvertXtoDVD and will be watching it on a conventional DVD player with a "regular ole" CRT television.
No matter what tool/app is used, it/they cannot make up quality--trash in-> trash out..
Since you're using CXD2DVD, I would use the quality advisor..It'll give you the 'Green Light' when you've chosen a given setting (best results) for your particular project..Try different settings and see for yourself what works best..