Unless the competitors increase the whole market (increasing total value) or—as is plausible with a cryptocurrency with netomwork effects—the lack of a single clear choice reduces the overall value of the market compared to a don't clear choice that everyone uses.
Not quite like a stock split. In stock splits its almost guaranteed that the total valuation is similar.
This is wild, wild cryptoland. At the moment both Bitcoin and Bitcoin Cash are rising - so a lot of "free" money (at least in the short term.).
For now, two coins is better than one :p
EDIT: allright, Bitcoin Cash has been declining for a few days now. However, it still has quite a bit of value that has not disappeared from Bitcoin's value.
By that point BTC would most likely go down in value. The more people who use BCC, the more likely it is to overtake BTC. If less people use BTC, there won't be enough demand for it to maintain its current price.
Why would BCC be valued that high? Because of the protocol redesign? Why bother with the fork when you could start a new network and announce the Genesis block start time?
Ah yes, keeping the sha hash vulnerability open for ASIC mining attacks is not a priority? Empty block exploits not a priority? Thousands of coins have been minted to worthless "proof of work" exploits and early adopters.