Allow me to bring this thread back on track
(BTW Jessica Alba is hot
I'm not too sure you listened carefully enough if you thought the E4c and E500 sound similar. I urge you to listen again, this time for a longer period of time. The E4c and E500 sound different to me even though they both have the Shure sound signature. I won't tell you what to look out for in case it biases your listening/opinion. It doesn't take golden ears to notice the differences, which aren't that subtle.
Did you not also find the E4c more detailed and refined in general? Coming from Etymotics, I think the best introduction into the Shure line-up is indeed the E4c. The E500 may be too drastic a change.
Of course, YMMV