Good idea. You want to keep your regulars happy; however you may want to think of telling them that you will 'hold' their rate for say, 3 months, then after that the rate will increase.
I don't what you do obviously, but with my regulars I don't clock watch so they get extra time. This keeps them really sweet plus I'm enjoying myself anyway so I don't mind.
For example, rate-wise, I recently changed my 90 minute rate from 150 to 170 and no one has complained.
In saying that, I would rather have a regular client at a lower rate than not have him at all. I find that gents don't really mind. Another one of my regulars got an 'introductory' rate from me and I told him the next time it would be extra and he did not mind at all.
I think it all boils down to the relationship you have with clients. I see no harm in having different rates for different gents where you know you have a guaranteed income.