I was specifically addressing what you quoted from the Council of Nicea. If the question is, do I agree with the Council of Nicea that the clergy shouldn't practice usury? Then my answer is yes, I agree with the Council of Nicea that the Clergy shouldn't practice Usury.
Usury, loaning money at interest, was forbidding in the Mosaic law.
Leviticus 25:35-37
But it was only forbidden for Jews to charge interest to other Jews. It was perfectly fine to charge interest to a foreigner.
Deuteronomy 23:20
If you are an observant Jew then you are breaking the Mosaic law if you loan money to another Jew and charge them interest.
The New Testament doesn't address Usury much at all other than to acknowledge it exist. In the parable of the talents the man who left talents for his servants admonishes the one who didn't at least invest the talent in the bank so he would have made interest.
Matthew 25:27
Having money in the bank is a form of usury as you are letting the bank use your money and they are giving you interest in return.
I think the overriding principle for Christians is to do everything for the Glory of God and for the love of our neighbor. That means, to me at least, to do what I can to help people out of poverty instead of doing things that will keep them in poverty.
There are times when providing a loan to someone can help them out of poverty. I just watched It's a Wonderful Life on Christmas Eve. That is a great allegory of how loans can help people escape poverty. The Bailey Building and Loan would provide low cost loans to the Citizens of Bedford Falls escape from the slum lord, Mr. Potter. The Bailey Building and Loan wasn't getting rich from interest, instead they were using the interest to provide more loans to others who need help.
At any rate, our modern definition of usury is not just loaning money at interest.
It is the illegal action or practice of lending money at unreasonably high rates of interest. I believe that is something we all can agree is bad, be it from clergy, an individual, bank, or car title loan company.