Yesterday I was half way through a print job and the 0.4mm nozzle that came with my Ender 3 clogged and stopped printing. I cleaned the nozzle and bowden tube, and it's printing fine again.

Is this a sign that the nozzle is starting to wear out? Should I proactively change the nozzle after a certain number of hours of printing? Are the cheap nozzle packs on Amazon OK for PLA and PLA+? Or should I consider investing in some premium nozzles?

Thanks,
IM

Thanks! I ordered an OEM e3d nozzle and I will give it a try.

Also, make sure your bed didn't creep up some.  Mine does sometimes.

I pretty much see nozzles & bowden tube material as consumables.  Eventually, cleaning nozzles gets to be more trouble than the cost of replacement. I generally replace rather than clean one that has started clogging, mainly because it is quicker & it seems like I am usually in the middle of something when it happens.  

Also, over time the portion of the bowden tube down near the back of the nozzle will degrade & deform (quicker if you are running high temps) - this can create issues as that little reservoir can throw off metering of both output & retractions, tending to screw up finer details. If the output opening at the end of the tube isn't round & the same size as a new tube you have hit that point & need to trim back to a fresh bit of tube.  You can also expect to eventually see a tar like material building up on the outer surface of the tube down towards the nozzle (again, sooner if you are running higher temps or don't have a good square cut end).  If you are getting to that point (tar buildup) you want to trim the end of the tube back to clean material (making a good square cut) & remove any build up that may be within the hot end. One method of cleaning is to pass a length of tube material through the hot end (with the nozzle out) until the tube passes without restriction & stops showing signs of the tar. You can also use something like a 4mm brush.
If the tube is too short to permit trimming, it's time for a new tube.    The sooner you catch this sort of thing, the easier the clean up.

nikdfish, has the right idea, the Bowden tubes, PTFE liners, and Nozzles are consumables and you should plan to replace them periodically.
So far my Mk3 like to get a hot end rebuild about every 1000h or so, although if I wasn't swapping materials as much I would expect it to be reasonably higher.

To add to the higher temp thing, frequent swaps between high and low temp materials will also toast nozzles.
You end up with either burnt low temp material coating the inside of the nozzle. Or high temp material coating the inside of the nozzle that didn't fully purge when your attempting to print low temp materials. Either way the coating will keep the material from transferring heat properly and lead to the hot end backing up.

Also be careful of fiber infused, or glow in the dark filaments. If it contains a material harder than brass, it will rapidly wear your nozzle. In those situations you really do want a harden or equivalent nozzle.

Regarding changing filaments, I've lately started using the higher temperature of the two filaments (old/new) as the loading temp to use when changing filament.  I seem to have fewer issues doing it that way.  Also I will use cleaning filament (super wide temperature range) in between when changing between filament types like TPU & PLA.