I am 62 and can still hear 14000 cycles on a good day. Before I dropped the dime on the speakers I have now I asked on an audio forum if they were worth my while at my age and quality of hearing. Good speakers do a lot more than reproduce the frequency extremes, I was told. They reproduce better ambiance, image better, have better dynamics etc., etc.
So I bought 'em and they did sound a lot better even though I could not hear the highs that my previous speakers did not have.
The best tweak I ever did was to put dedicated power circuits, with isolated grounds, to the components, eliminating all the noise on the household power supply.
Dead quiet background now- no hiss at max volume at all.
As far as breeding stuff in an aquarium, I left a 35 gal alone after the last fish died- for 5 years now. It grew some interesting stuff before the water evaporated to the point that the remainder was so "hard" that nothing would grow.

One of these days I am going to start it back up and put some "easy care" fish in it to inspire my grandson, who has shown an interest in fish. He has two small tanks, one with a beta, and another with some platies. He is 6.
Oh.... and you are always an audiophile on a budget unless you are filthy rich.

In th early '70's I priced out the most expensive system you could buy.
It was $65,000. Now you can spend that on a couple of cartridges for your $200,000 turntable.
I get the imaging thing. I had a set of Vandersteen"s that imaged very well. The advent of family and downsizing personal living space had me make some changes back then. Then we went through the surround sound thing. I have an empty house (well, I still have my cat) and am back to 2 channels. My current equipment won't allow me to appreciate the installation of dedicated circuits. I do still use my sorbathane feet under my DVD/CD player.
That's awesome about your grandson! I think fish are a great way to learn many of life's important lessons.
Turntable? I have one in my microwave.