I have like most of you asked Ning to do something about this issue of only being able to resend an invitation 50 emails at a time, but now if you've tried to resend an invite lately you would have discovered that clicking the select all box not only selects all 50 contacts on that page but also shows a link that allows you to select all invited contacts to either cancel invite or resend it.
I stumbled on this before hearing any word of this (if any word of this has even been mentioned yet) because I recently changed my point to domain access to point to another website of mine hosted by Weebly, and created a sub-domain on the same domain and pointed that to my Ning network. So after doing all this it hits me....those persons invited by my members will no longer have a direct signup link in their emails. So with my mind already set for the long drawn out process of reinviting 50 members at a time until I reached the end or fell asleep, I was pleasantly surprised when I discovered this update. Yey Ning!
Awesomeness ! Thank you Ning team.