Charge for my coaching? When is the right time to increase fees?

I have been coaching for several years, mostly business coaching with a bit of life coaching too. I do not have a problem with accounts receivable. In other words, I get paid for my work.

When is the right time to increase my fees? Some say I should charge more. My husband says to not mess with a good thing. I usually feel quite good about my fees… that I provide value and my clients appreciate our work.

Should I charge higher fees with new clients and leave the existing as is? or create a new model?