Selling half of your BTC is also a good idea since you already gained the profit from your initial capital. Joining or investing on Alternate Cryptocurrencies can make you more versatile within the Cryptocurrency Industry and that move is also another way to involve yourself into a wide variety of Cryptos.
Investing in random alternative currencies will not bring versatility but high risk. From the way i look at the market situation right now, all the major alt coins have rallied a lot and even the potential ones are trading at their all time high barring a few coins and you cannot sell your bitcoin and then invest in those expecting it to rally further 
.