I was searching a setting restrict certain groups to give out reputation points but I couldn't find any :ermm:

It is a must-have setting to have for a reputation system in my opinion :P

Hopefully this and other reputation enhancements that have been thrown around will be added

Yep, no option to do this. Setting the max and min to 0 means Unlimited.

I suggest for the settings:
-1 = unlimited
0 = none
1- = may give that number of rep points (1 is 1, 2 is 2, etc)