They are not reversible, they are the nature of early 90's technology, they are not irritating unless you are an OCD freak.
not just the early 90's if we looking to some other products recently released by a handheld manufacturer named sony, where the dead pixel coming already as a factory setting.
@RCduck:
Can a dead pixels become very irritating? > it' depends in which color the dead pix turns for permanently. when the pix is white and the background black (or other dark colors), then it could be quite irritating or disturbing in terms of a proper working collectors item. but not big impact on the gameplay etc. as long there not tousends of pix-graves on screen.
And are they reversable? > no
Or do i overestimate the problem? > it depends on the person itself. if you spend $700 for a collector item, it may really could hurt you every time you get confronted with this, more to say cosmetically problem.