The wisdom to attack bonus is a pretty powerful ability. One of the reason Solaris might be overpowered is because all his abilities revolve around his wisdom. He has the feat that increase his attack, he gets it to his AC because he is a Saint, and he gets it to all his spell abilities as normal so I really don't have to worry about pumping any other score. With the bonus to wisdom from the vow of poverty, saint template and adding points ever 4 levels his wisdom is extremely high and it effects every aspect of his character. Part of the reason the saint template is so powerful on a cleric is because of the Wisdom bonus to AC since the cleric already is focused on Wisdom anyway it will be extremely high. That is one of the reason this ability is not as powerful on a monk. So buy creating a domain that gives a wisdom bonus to attack for a cleric you run into the same problem.
Also DM when reading the ability immediately capped it for natural wisdom and not to include bonuses from magic items etc. The fact that is capped tells you something.
Here is what I would suggest:
If you have it be a permanent ongoing bonus then I would have it replace Str not stack with it. Also if you are going to do it I wouldn't cap it. Is you have this ability then I would have be all or nothing so include magic items etc. I think capping for natural wisdom creates unnecessary confusion. Sink or swim with the ability that is created.
However, what I think would be best is to have activate as a free action turning attempt. So you activate you turn attempt and you get a bonus from your wisdom for a certain amount of time. Maybe for 1min.