Out of the 1000s altcoins, there are quite a number with use case. So, I dont think all altcoins are useless actually.
Is it worth buying altcoins now days? I guess no, because all of them excluding tether are following bitcoin price chart. I mean if bitcoin is going up or down, altcoins are doing same.
I do think it is worth buying altcoins. Most of the better altcoins dipped hundred to thousand % from the ATH, whereas Bitcoin dipped around 80%. I believe when market recover, the altcoins will be pumping harder.