Plan to change the review fee on a niche directory, should i or is it necessary to let your current customers know the update? or just send email to notify your returned customers?
I'd wait until their listing comes due for renewal. If you send a reminder of expiration, I'd include the new price there. You might also want to add a bit of sales info like, last year was an exciting year, blah, blah, we saw more traffic, better SERPs, etc. - in other words an informative but non-apologetic reason for the increase. The only problem that I can foresee is if anyone is paying via an automated subscription.
I agree with YMC. That's exactly the method I use when raising prices on my membership sites and it works every time. Sure, a few people will always complain and a few will cancel but the overall profits make it worthwhile. Best of luck to you