I agree, later experiences can't compare to early ones. But I think they can be just as fruitful.

Like I got baked and went to the Independent party caucus last week and it was fucking awesome. I made some seriously profound observations about human nature and American politics, and personality types.

Wear sunglasses, walk around with a 'scary monster' sign hanging from your chest and a black leather glove on the wrong hand and challenge strangers to hockey games - confrontational art, man. Act out a script with some friends.
Be creative and spontaneous - art and grass are like two peas in a pod.

I think you have to find new and novel things to do - go to an art museum baked or ride the bus (that is fucking awesome). I've always been the 'silent observer' type, and lately I've been observing on a whole new level. But, I suppose, even this will get old and I'll have to find something else to do, or maybe just stop smoking for a year or something.