There are some acts who use audience mics just for their IEM's because they feel so isolated. I can see that.
Agreed
To add space, add an audience mic. You could even have one permanently setup if you have a head rack. Just point towards the audience, and send that signal to the board.
I would avoid reverb because I don't think it is that you have too clean of signal, it's that you don't have enough ambient noise, IMO.
Agreed again, reverb can help but it's definitely not the same as having audience mics. My church has a couple of campuses and I play at both. At both we all go direct, and use IEM's with Avioms on stage for our own mixes. I get a good sound at both because I learned to spread everything out in the stereo mix (hard panning the two electrics, soft panning my bass and the keys which are run mono, and medium panning any background vocals). One campus gives us reverb to add to the whole mix, and the other has two room mics set up which I hard pan.
I get my best mixes in the ears at the campus that uses the room mics, BUT there are times when we have a volunteer sound guy that's not as good as maybe another one, and the ears don't sound great possibly due to the room having a weird mix (though there could be a number of things causing that).
One other benefit of room mics imo is that you can get a lot more of the low end in your ears than you do with just signal fed back to you from the board (this may be because our board doesn't send an EQ ed mix to the ears, but also may be due to having subwoofers throwing out lows into the room that you just can't hear over the harmonics of a plain bass signal.