Bitcoin competition: What's stopping someone from developing a better code/coin?

[Wagner2014]

Two major concerns I have re bitcoin:

1) security; and

2) competition.

Bitcoin by all accounts is the product of genius, but the code can be studied and improved like any product. Any comments on this possibility. I realize ultimately a currency is valued due to wide spread use and acceptance.

[Cyberdyne]

Q. What would shareholders of Coke do if they were worried about competition from Pepsi?

A. Buy some Pepsi shares.

Similarly, if you're worried about an alternate crypto currency competing with Bitcoin, then diversify into that currency you're worried about.

I have BTC, LTC, and a small amount of others,. not that I'm worried.