My rear sight assembly is actually quite tight to move, but it's adjustment stays put.
Regards top 10, pursuant to your question, I humbly present;
1 new spring guide rod
2 new springs from Wolff (google it)
3 National Match sights
4 do you need a new flash eliminator? (I do, but the gun shoots well as-is)
5 a nice shooting sling (I picked up an Uncle Mike's copy of the old leather USGI sling)
6 get someone to unitise your gas tube and hand guard clip
7 if you're seeking accuracy, get set up to reload your own ammo. it's the trick with these units!
8 feed your brain; attend an M14 clinic. ...I havent yet...
9&10.... screw 9 and 10. Short of spending your money beyond what I would personally, I think that right there's a good start.
Ok, fine, 9; I think the Norinco stocks are about thick, so I'd also replace it with a USGI unit, wood, because I'm a parkerising and linseed-oil kind of guy.
9 times .02$, = 18 cents worth there I reckon