So, sure, it's nice to have more convenient string changes. But, I don't want cheap tuners, no matter what. It's one of the big things that tells me immediately whether the guitar I'm playing is cheap or expensive. I used to think Klusons looked cheap and old, when I was a kid, but I have grown fond of them after so long playing. It's what's on both of my really expensive guitars (came from the factory that way), and I've never felt the need to change them because they've worked great for decades.
That said, if you've got a cheap-ish guitar and want to improve it, tuners, nut, and bridge are where I'd start (after getting a proper setup, and getting the frets in shape, of course). Also, while I'm ranting about the onion on my belt...bone is a poor choice for nut/bridge material. It has wildly inconsistent density and hardness, and just plain isn't as good as modern materials (and we can note that many of the very best and most expensive guitars today, like PRS, do not use bone).
Depending on the specific guitar I'd also look into swapping the pickups. That usually gives the best sound improvement but does nothing for the playability. Luckily, the playability of a lot of cheap guitars today is very, very good.
I agree that bone is a terrible material. It's only still used for historic reasons, I think. Guitar players are a notoriously superstitious bunch and often times dont necessarily want the best when they can instead have what we thought was the best in the 70s.
The quality improvements that come from heavily automating the process are hard to overstate. CNC machines, and improved metal fabrication methods, have revolutionized guitar making. They're still putting cheap hardware and electronics on the low end stuff, and it shows in the longevity, tuning stability and some other areas, but as you note they mostly play really great right off of the rack.
They're still using cheap-ish wood that doesn't age very well, also. Fret sprout and various sorts of warping is, as I understand it, still much more common on cheap guitars. My 29 year old Schecter has never had a setup or adjustment, and still plays beautifully (frets are a little worn and could probably use a touch up, but still very little buzz). The G&L L2000 bass I have is 31 years old and has maybe had a couple of turns of its truss rod in the time I've owned it. I dunno about any other setup or adjustments in its life as I've only owned it for about half of its life. But, I get the impression that cheap guitars are needing attention within a year or two, mostly because the wood is fresher when they build them and so they aren't as stable.
My G&L ASAT guitar is actually a Tribute, so it's one of the cheapish ones made in Indonesia. It's in need of attention already (quite a bit of fret buzz even without really low action), and it's only a few years old, so it seems to bear out my theory. It's not a "cheap" guitar, and it's not poorly made, but it's not an expensive guitar, either, and I'm guessing the wood was aged/dried for a much shorter period than my American G&L or the Schecter. The only other American-made instrument I have is a Gibson J-45, and it's holding up very well, too, but it's much newer...a 2008, I think.
Even my Gibson J-45 has them; it hasn't always been common for Gibsons to use Klusons, and while the stuff Gibson usually uses is also fine, I prefer the Kluson style. They're aesthetically pleasing in a functional, not showy, way.
It's my experience that locking tuners do help with tuning stability but I've also seen plenty of guitars stable enough without them.
Even if they don't help a guitar with tuning stability, they definitely speed up the string changing process which is worth it for me.
edit: I've just noticed that the link in the parent comment is for "gotoh style" tuners, not tuners made by Gotoh, and I have to say I agree with you about the low quality of cheap tuners. That said, a good set of locking tuners should only cost you $50-$70. Not a bad price.