Which ones? There are hundreds of these things, and my personal view is that they're mostly worthless. I really don't think the hard part at this point is coming up with a cool use case for cryptocurrency, or even building the technology that works (though many of these alts have yet to even do that). The hard part is adoption, and my estimation is that almost all of them will fail at adoption. Time will tell, I guess.
I'd argue that BTC and ETH are both extremely overbought at the moment
You might be right, you might be wrong. It'll only be clear in hindsight. Which is why I don't time the market or trade. I just buy and hold for the long run. It's a small portion of my networth, weighted towards BTC and ETH, but I'm buying some other alts with 1-2% of my net worth (total).
In the long run, the cryptocurrency market will be worth $0 or trillions, so I'm not particularly worried about whether I got in when it was $10 billion or $500 billion or how it goes up and down in the meantime.