If you're looking to augment staff as a contractor, whoever hires you is going to want to compare your hourly rate with what they're paying their team — so it's going to be tricky to break through that ceiling.
But if you're working with clients who have problems to solve, and you're hired to solve one or more of their problems, what you charged should be tied to the financial upside that business will experience when all those problems go away. (e.g. pricing for them, not you and your former salary.)
I gave a talk last night on value-based pricing for my local Ruby meetup, and covered some of this: https://speakerdeck.com/brennandunn/value-based-pricing-for-...