How do I know when to change cartdridges?

I'm new to analog, having obtained a Rega P3-24 a couple of years ago. I'm wondering how I will know when it's time for a new cartridge. My concern is that in such a mechanical system, the wear-out will be gradual and thus hard to detect. Which is fine in a way: if I don't know it has degraded, then why should I care?
I have a Dynavector 10x5 now, which I believe is a high output moving coil. I've seen several people post that unless your budget is much higher, you should stick to moving magnet. If that's the case, what would be a good moving magnet cartridge to get for this setup?
If it makes a difference, I'm using a Dynavector phono preamp which is switchable for MC or MM and Audio Research tube amplification. And I doubt I would get approval from CINCHouse to spend over $1,000 for a cartridge.
Thanks for any guidance.