What would've really helped the 5c, in my opinion, would've been for Apple to make it free on contract. Heck, "free" was the buzz word of the most recent Apple event. Had they made the 5c free on contract and starting at $399 unlocked for the 16 GB version, that would've made some serious waves in the industry.
Why am I going to pay $549 off contract for an iPhone 5c with what are essentially last year's internals when I can buy a used iPhone 5 off contract in excellent condition for $200-$250 less on eBay?
If I'm going on contract, why not just pay $100 more and get the latest and greatest iPhone instead of what is essentially last year's model with a colorful polycarbonate shell?
If they keep the "c" line around for next year, I look for them to essentially do the same thing they've done with the iPads -- make the internals identical (with a slight clockspeed difference on the processor) and the only real differences would be polycarbonate vs. metal finish and perhaps screen size. Or maybe they'll ditch polycarbonate (and the "c" delineation) entirely, give it a new name, and make the only tangible difference screen size like they've done with the iPads.
If they give the "c" line internal spec parity with the "flagship" line next year, I don't expect the prices on the "c" line to change at all from what they are currently. If the internal specs were essentially identical to the flagship iPhone, though, the current prices would be easier to swallow.