There is nothing that will make you feel like an old MMO grouch more than hearing people get excited about the prospect of reusing content you saw enough of the first time around.
Naxxramas! Onyxia! Heroic Deadmines and Shadowfang! All the monster models that get recoloured, renamed, and reused! Scaling instances in LOTRO!
I don’t hate any of these things. There is a balance between nostalgia (Hey! I remember back in the day when we had to walk uphill backwards to get the key to blahblahblah) and burnout (if I ever have to see that fight again I’m going to rip someone’s arms out). But modern MMOs can’t afford to leave too much old content hanging around unused – it just isn’t cost effective.
Also, the new players hear the older ones talking wistfully about how the game was back in the day. They don’t see the annoying parts that get skipped in reminiscences, they just feel that they missed out and are being left out of the conversation.
I wrote once that after about 3-4 years, an online game would have to change or else it would die as the first wave of players moved on and the newer ones could never catch up. I now think that after 3-4 years, older players will be nudged to move on because smart devs have realised this fact and will then start to direct most of the content to the newer players.
So if your favourite game starts to make you feel old, grouchy, out of touch, and as if any new elements are no longer aimed at you … maybe you’re right and it’s time to move on.