For me the hobby is just a way to be busy. It's a creative process (setting up your tank and planning how it will look), it's a learning process (looking up all you can about the species you want to keep), and it's a meditative process to me as well. Sitting at my aquarium is more pleasing most of the time then sitting in front of my television.
I know, i'm a bit obsessed, but aren't we all here on the AA
I wouldn't consider it a waste of money, although it can become costly. I personally think it's money well spent. An aquarium serves many functions to me, so it's okey that a costs a bit more then your average hobby (although i could think of hobbies which are more expensive, but that's a different discussion).
It's an enormous pleasure to feel like you can set up your own little garden of Eden in the middle of your bedroom, livingroom, .....With fishies in wonderfull colours if they're happy. whiwh we can take care of if we learn about their habitats before buying them!
In short, no waste of many, no liability, wonderfull hobby.