For a full spellcaster, this will be a potential power increase; you're looking at up to +2 to all DC's plus extra spells per day. On its own, it's not worth changing CR over. It could certainly add up with other things and you may want to consider adjusting CR in that case. For non-casters, it's not as big a deal and definitely something you can gloss over.
If you just refrain from placing 18's in primary spellcasting attributes, I don't think you even need to think twice about this. If you do put 18's in primary spellcasting attributes, just apply common sense as to whether the resulting DC's are reasonable for the CR.
Depends on the point buy system. If they've got higher than a 15-point buy, their APL should rise by +1.