In the same vein, instead of lost-forever achievements, what about mutable ones? To sketch a basic illustration of what I mean, say that you got an achievement for the first enemy you killed in a game, but the achievement was different depending on what weapon you used?
Coming from a hardcore completist, this sounds ok. For example, if that achievement was "__ murderer" and I got the achievement using a chainsaw so I had "chainsaw murderer", I wouldn't be concerned about not getting other named achievements if the achievement's name didn't affect gameplay elsewhere. If it affected even something small like speech, I would probably be concerned cause I know there may be other interesting variations of the speech had my only-nameable-once achievement been named something else.
In the vein of "adding replay value", would a lost-forever achievement of "Do X on your 3rd (or whatever) playthrough" be a dick move? You know it's coming, you have a chance, and you're also raping the hell out of any replayability you have?
This would add replay value because players will play up to their 3rd playthrough to do something, but it wouldn't be a good kind of replay value. They're forcing themselves to play more to get 1 achievement which is only acceptable if the game itself is good. The level of dickishness is dependent on a number of factors such as how hard the achievement is to get/how long it takes to get to that playthrough/how fun the game is/how beneficial the achievement is, etc, but since you know it's coming, it will be less dickish.
I knew a game like this, and the achievement was acceptable because you know it's coming and the game was fun and you knew how much you had to prepare yourself beforehand.