I’ve dealt with a few of those little cracks myself, and from what I learned, it’s less about whether they look small now and more about how they behave over time. Hairline cracks might stay harmless for years, but they can also become a spot where dirt, algae, or even minerals start collecting. That’s usually when they start to stand out more and become annoying to clean.
If you’re planning a full resurfacing soon, it’s probably fine to just monitor them and keep your water chemistry balanced. But if resurfacing isn’t on the horizon, I’d do a simple patch, it’s inexpensive, doesn’t take long, and gives you peace of mind that nothing is sneaking behind the plaster. Kind of a “better safe than sorry” approach.