I never quote hourly rates either.
Things like hours and sketches have limited value. A solution has almost unlimited value however. As designers we are in the solutions business. Sometimes solving problems the client didn’t even know existed.
I use an hourly rate though to help calculate a flat fee though. A friend who was a former account manager recommended adding 10% to that rate with each project to see how far it could go. Solid advice. I was following it until I got to my current role where I don’t really have the mind space to take on extra work other than for Icon which is more of a passion project type of thing.