ZEC is trading over 1BTC even now. Of course it's coming down! I have high hopes for ZEC, but nobody would expect its value to supplant bitcoin in 48 hours.
No, what's happened is that the initial prices have been driven by scarcity, which is a side effect of the slow start.
There were only approximately 100 ZEC in existance after the first 24 hours and by volume every single one of them was traded many, many times.
At the end of the month when we're seeing 7200 ZEC produced per day, it will be more realistic to expect a price that is fractions of a bitcoin. That won't be an indication of failure, and it won't mean anything for miners by itself.
Whether it is 'worth' mining will be due to a comination of factors, value of individual coins being only one of them... and we will all have to wait and see how that turns out.