Unless the new hole is directly over the old hole, there is no issue.
Seriously, sometimes Ive had to drill partially into the plastic plug that i put into the old hole. the rule there is that if the new hole doesn't go more than 50% over the old spot, there is no worry. If there is a metal laminate you can drill for days into that
there was a post on black diamond's blog regarding strength of new holes. they pretty much figured that anything pat 8mm was as good as it gets. anything closer than that and your likelyhood of bindings ripping out goes up by about 10% per 1mm or something similar.