When should you get rid of a guitar?
This is a tough question that is not easy to answer.
I'll start this one off by saying that if you still own your first guitar, such as I do, don't get rid of it. I don't care if the guitar is a complete piece of crap, barely plays anymore or is even broken. Don't part with it. That's your first guitar and you'll never have another.
When it comes to every guitar after that however, the answer on when to get rid of it depends on whether it represents a significant part of your life or not.
An example of a guitar worth keeping other than your first is, "Yeah, that's the guitar I had when I was in school." If the guitar has been with you a while, traveled around and reminds you of good stories that involved it, then yes, it's significant and you keep it.
Another example would be a guitar given to your child that later gave up the instrument, but you kept it anyway. That instrument probably won't be played regularly ever again, but it doesn't matter because it was part of your kid's life, so you keep it (preferably away from the kid so he doesn't go and sell it.)
Aside from those examples, if you have a guitar that is used only as a tool to make music with, it doesn't hold significance in your life nor anyone close to you, and you barely play it, get rid of it and get another different guitar.
Since the late 2000s I've bought and parted with several guitars. Mostly Squiers. I buy one, play it for a while, and if I lose interest in that particular instrument, I get rid of it and get something else.
Right now I'm all about the Jazzmaster. But I may get a Telecaster at some point. It might be a Squier. Or maybe a Fender. Or maybe something totally different like a Schecter PT (which looks awesome in gold, by the way.) And I may purposely get a Tele with humbuckers in it. I love my single-coil pickups, but there are times I like the blare of the dual-coil.
I don't plan on parting with my Jazzmaster. But I do plan on getting some kind of Tele in the future. If that Tele proves to be so awesome that it becomes my #1 guitar, then yes, I would part with the Jazzmaster. That's a very unlikely scenario, but it is possible.
The point is that I'm willing to try different stuff, because let's face it, it's easy to get good guitars cheap these days. However, I'm also a believer that one should not own too many guitars, because then you're hoarding.
There have been times when I've parted with a guitar, only to buy another of the same model later because I missed it so much. An example is the bass guitar I own now, the Yamaha RBX170EW. I used to own a RBX170 non-EW version, and I realized how dumb of a mistake it was when I traded it out and tried my hand with a short scale bass guitar. A few months after owning that short scale, one day I saw the new EW version of the RBX170, it looked great and it was the bass I wanted again, so I quickly ran to Guitar Center, traded out the short scale and got my bass back, this time in a better looking version. Everything worked out well there and the price was definitely right...
...but for all I know I might get rid of it and pick up a Jazz Bass in the future. That could happen. Again, an unlikely scenario, but hey, I play whatever works that's priced right, feels right, looks good to my eye and sounds good to my ears. That's all that matters.