Why "expensive" or "cheap" matters at all? If you have certain amount to invest, you can buy 0.1 BTC or 1000 unknown-coins. What is important if it will be +20% or -20% tomorrow.
The important part is that most coins are expensive, having 1,000 coins would be worth a lot of money. A 20% increase would be a nice investment.
I mean if one invests 100$ and price increases by 20% - it is not important if he/she owns cheap 1000 coins or 0.01 expensive one. Total balance will be 120 USD still.