Just wanted to add a few things... I never reco anything I don't have direct personal experience with. Based on what you said you wanted, I reco'd the iM716. I've never heard the e4c's but I do have a lot of "life" experience (which may or may not be helpful - you be the judge).
If you really (I mean REALLY) loved the sound of the e4c's, if they really did it for you, then buy 'em again. But if you have any doubts, then consider your options and buy something else. If you do buy something else, let it be something that that would be a step-up in SQ. Sideways steps can be disappointing... so let it be something that you know would be better.
I (also) own UM2's but can't say how they would differ sonically from the e4c's or if they would be worth the $100. price difference to you. I can tell you what I hear. Source is a Meizu M6SL. I freely use a lot of its sonic adjustments.
The UM2's are a big sound (almost in your face). They're very sensitive. It takes little more than half as much gain to drive them to the same volume as the UM1. You should get ton's of volume from them (yeah I know, not a very scientific statement). The midrange is very full, I think too much so - and I back down on the center frequencies a bit with the EQ. The top end is soft. All the highs are there but a little rolled off. You can bring out a bit more sparkle with an EQ. Others have also said they're soft on top and I'd agree. They certainly don't have the top end detail and resolution of the pod-modded iM716's (which I've read, don't equal the Ety ER4 P or S). The AL's still do have terrific treble extension and resolution. The UM2's don't equal it, but surprisingly they hold their own in other ways. The bass is excellent, it's defined and there's a lot of it. Depending on personal preference (using an EQ), you may want to decrease or even increase it. Additionally, UM2's have a lot of inner detail. Harmonically I can't find fault with them. Some have called them "fun" to listen to, though not the most accurate. Maybe the forthcoming UM3's will claim that title. I can say that they're a balanced, forgiving very easy-to-listen-to sound. I think they're the epitome of fatigue-free listening. You can listen to them all day - happily. I think that's a good thing. (IMHO), I think that IEM's that are unforgiving, that do present the last word in detail and extension can be sonically fatiguing after long periods. But this is a personal call - you know your own preference.
The UM2's offer other intrinsic advantages. They are supremely comfortable to wear, especially with the soft foam comply tips. You can (if necessary) sleep with them on, they don't stick out from your ears. The cables are twisted (not too stiff) and completely non-microphonic. And, if you break 'em, send them to Westone in the USA their CS seems pretty responsive.
I didn't plan to write this much but I hope it helps.
