As already pointed out each of the IEM's mentioned is considered 'the best' by some, and some of these people have tried several of them, like me. And yes, only a (very) small percentage of them have custom tips or shells.
Re: the cons you list the jury is still out there on the so-called recessed mids. On the other hand, I believe that if the SM3s do not improve with amps I'm sure most people would see that as a big plus, unless you already have an amp and are the type who enjoys using & carrying one around - on the whole I think portable amps are snake oil and not just with the SM3s; my experience was the same with the UM3X, W3 & ES3X, ie NO improvement whatsoever. You did, however, forget to mention the build quality, which does worry me a bit.
As for goods from outside the US, I specifically mentioned a few Western European countries and did NOT mention Asia, which obviously a lot of people - not just in the US, btw - look down on, particularly China.
One reason I found the UM3X so good was precisely the lack of an initial WOW effect, yet they delivered excellent, understated SQ along the whole frequency range. The treble seemed perfect to me, never being too much, although sounding a little recessed with some poor recordings or older classical recordings. I often thought thank God they don't have more treble as that would have made me sell them very quickly. But, with good recordings, eg from ECM or some remastered music by other labels, the UM3X delivered great sound and to these ears that sound was VERY exciting - exciting in the sense that nothing seemed boosted, not even the mids as some people claim, which to me were the best mids I'd heard. And the instrument separation was quite something else. The UM3X and ES3X have been the only IEM's that are 100% non-fatiguing after extended use. Also, I never found the UM3X as narrow sounding (soundstage) as some claim. Hence my shock after I listened to the IE8s, the claims being the sounstage was much bigger than the UM3X's.
I've often (too often, actually) seen people comparing the SQ from a particular IEM equating excellent sound to that heard in live performances. I'm sorry to say but well over half the concerts I've attended - and I've attended quite a few - have suffered from poor, or very poor, sound quality.
Anyway, I decided to try the SM3s precisely because they seem to share a few qualities with the UM3X, and I wonder if perhaps the SM3 might even sound a little better.
The UM3X only came (don't know if that's still the case) with comply tips, and although some people did try other tips -- I myself preferred the soft silicone Westone/ Shure tips by a long shot -- they didn't seem to try so many as seems the case with the SM3s. And the praise for the UM3X went well over the FOTM period. Perhaps it's a design flaw, after all, or like I said perhaps some people are desperately trying to like the SM3s, and trying to get a different sound, ie not the intended sound Earsonics meant for them.
I believe you meant recessed highs, not mids. AFAIK no one ever claimed the SM3 have recessed mids. 
Concerning live concerts, I believe it depends on your preferred genres. Classical performances can have wonderful SQ in a suitable venue. Most Jazz and Folk concerts I've been to had pretty good SQ too. Sadly I can't say that for the vast majority of Pop/Rock concerts I've seen.
I haven't heard the UM3X, but from what you've posted about their qualities I think you made the right decision, going for the SM3. Hope you'll like them! 
) than how they actually sound.
