What is the difference of a pre-ban ruger mini-14 versus a new mini 14?

Answer 1

None, really. I think it was 2005 or 2006 that they began putting Ghost Ring sights on them, and in the last couple years, Ruger has tried tightening the tolerances a little to make the design more accurate. But the design itself really wasn't affected by the Clinton ban, because the design itself was never classed as a "civilian assault weapon" by the BATFE.

The only difference you'll find is in states such as New York, which have ongoing so-called 'assault weapons' bans. On a pre-ban rifle, you'd be allowed to add two or more of the cosmetic features which the BATFE determined made a 'civilian assault rifle', such as flash suppressor, bayonet lug, prominent pistol grip, barrel shroud, and collapsing/folding buttstocks, whereas only one such feature would be allowed on a post ban rifle.