Not a good time as the price of bitcoin is rising now. When bitcoin's price is begin to fall, then you can buy some good altcoin.
What you said it true but no one can predict when BTC prices can fall. But if it falls then in a day more than $100 fall then one will miss the chance of buying at a lower price. So if one decided to buy any coin then start accumulating in small quantities then finally you will get a better average price.