I've been thinking about this one for a long while now - I reckon that the brain works in two distinct ways, reflexive, where the responsive action to a stimuli bypasses the 'what the f*ck' part of the mind and goes straight to the 'skinless bucket please even though I know that KFC = catastrophic liqui-poo as the body tries to throw the chemicalised fowl as far away as possible as quickly as possible', and cognitive, where the mind takes it slow, such as 'those whirling blades look fun to touch but I'll wait and see if someone else does it first'.
Thing with this is, the brain is a clever little cauliflower and rewards the cognitive behaviour with a rush of fun juice (endorphin, not the self-pleasuring kind). So when you do something for the first time, or while the brain is still unsure about it, you get the little squirts of endorphin. That's happiness for all those middle class workaholics who have forgotten what it is.
So we associate certain actions, from when we did them for the first time, as fun. However, when the old brain decides that there's nowt scary about what we are doing, it switches the behavioural response to reflexive, which takes place in another part of the brain which locks behavioural response down to fire here, you there. This doesn't need squirts of fun juice, as we already know the outcome, so the stuff we did before that gave us a rush now doesn't. Being daft, endorphin ridden animals we don't get this, so we do more of the now-reflexive action to try and get the same level of fun juice. But nada.
Familiarity breeds contempt, but I reckon it would be more accurate to say 'repeated actions produce less training endorphin as they are incrementally performed to the point where they are hard wired and produce no internal stimuli to encourage action'. Not sure that will slip into common usage, but what the hey.
My point is, the more you do something the less simuli the brain will produce. Unless that action would cause danger or excitement (I imagine repeatedly throwing yourself into oncoming traffic would never get old, up until the point the cars won of course).
I'm guessing nostalgia is now a thing of the past.