Hi there.
I think you hit a good point and a fair way to increase your rate while keeping your regular customers. As you say you scratch my back and I'll scratch yours relationship does work for me. It's swings and roundabouts also, I have a clients who pays £800 per double page spread flat rate. And because it's 3D landscapes of battle fields, I just love doing the work, and I can get it done in 3 days but I could easily spend a week doing it. And for me also it's not about making the money I truly love my job and sometimes it doesn't seem like work. As long as my mortgage is paid and I can have a holiday when I want and having totally flexible working hours; as you are your own boss, just having that little bit of freedom and not having to account to anyone else is what it's all about for me.