Investors tend to diversify because they want to lessen their risk of losing all of their money.
Diversification is good but overdiversifying your capital isn't good too so at least learn to balance and know where to invest your money.

In your case, 0.4 BTC is a big amount already. Diversifying is a good thing if you have a spare money. I would suggest to at least diversify into other coins but don't forget to put some in Bitcoin. If you are asking cryptos only then putting some in top altcoins would be good like Ethereum or ChainLink or Cardano. Now if you thought of investing outside crypto to diversify your portfolio then investing in real estate will be good too .