RuleO'Thumb, <1 yr / <1% of possible market, go crazy. >1 yr / >5% mrkt, change ID as few times as necessary. Learned behavior.
There's a lot of caveats and provisionals there. But logos deal with learned behavior. Reading is a learned behavior. And people learn to read words, not letters. And when you're reading a book, you're actually reading groups of words, not every letter. Your logo is the lingua franca of your business. People learn it. The entire look becomes your name in the way they process visually. Now, words actually have a lot of readability and you can play with the legibility and still maintain recognition of the word.
Logos function the same way. However, change too much on the legibility side and you break the readability.
So, first up is if it's a logotype (ie. your logo is the name of the business, or trade name), you're a little looser on the rules. Logotypes, which the name is primary, are easier to relearn and transfer in the consumer's head.
If your logo is a mark (as in a graphic without any type), lean toward the conservative end of making changes. Unless your business is in dire straits, or you've gone up 300% and are now making doodads as well as widget, just say no. If you've dropped 50% and used to make doodads but can now only handle widgets, that's also a reason.
Just because you're sick and tired of seeing it isn't a reason to change. Your customer, if they're a very, very good customer will see your ID about 2% of the time you do. They aren't tired of it, they just got used to seeing it.
And then we go into the argument about what is and isn't really a logo and what is a graphic. Some business people mix those terms freely, and it's permeated out into the general public. They aren't the same.
Such as John Scalzi's "Whatever" type at the top of his blog. Some people will see that as an ID of his site (and when he changes there's a good portion of his audience that gets upset because they have to relearn it). It's actually a graphic. It can change without changing his exposure in the market place, and whatever is a destination, not a product (insert marketing screed about what is what and what John is doing with Whatever, blah blah, it's still not a logo, okay?).
AT&T's globe is the alternative version. How many of you are old enough to remember when that was a bakelite phone (or a bell - bwahaha that's what they were Mom Bell) up there? Yeah, they changed in the 80s to the globe. And they haven't changed (much) since then (they've widdled at the edges).