It can always be difficult to get the right balance, I've known freelancers to fail due to the lack of support they can physically give to clients. The nature of freelancing is - be in a position to accept work all the time because you never know when work is going to dry up! The trouble is there are only so many hours in a day! In situations like these it is better to raise or lower your prices in line with supply and demand, this way if your client really wants something they will pay for it and you will have the funds to outsource if need be, thus keep your client happy. Also over time you can weed out your 'not so good clients' and only work with your 'good clients'. A slightly different take on your original post I know, but I thought I'd throw it in anyway. I like your idea of a reduced rate on the next job - it gives your clients the opportunity to reclaim some of your time, it also gives them a good reason to stay loyal, that is as long as you want loyalty from that client.

I'm ready for the dreary and gray days to be over. Enough of this snow already. These pictures are great!