dSLR Backup: Enthusiast P&S or Mirrorless?

The question says it all.

I love my D300 and its stable of lenses, and it provides me with all of the technical capability I need.

On the other end of the spectrum, my tiny waterproof compact gives me a camera that I can take in a kayak without fear or hesitation.

Third, my smartphone is a constant companion that takes nice photos, is always on hand, but is limited in many ways.

What I'd like is a camera to straddle the middle ground between these: more compact & portable than my D300 kit, better IQ and controls than my waterproof, and better output, and controls than my cell.

While I'm not ruling anything out, the decision, at this point, it pretty much between an E-PL3 w/ kit lens (eventually supplemented by the 14/2.5 and 20/1.7 pancakes and a tele zoom), or a Panasonic LX7.

In support of the m43 over the LX7, it's got a much larger sensor, interchangeable lenses, and longevity (it's a system, not a camera...if/when I want, I can sell the E-PL3 and get an upgraded body, keeping the lenses.  When the LX7 is gone it's gone.)

In favor of the LX7, it's (slightly) more compact, has more features (like in camera HDR, panorama, internal ND filter, etc.), and may suit my "take it everywhere" needs better than the E-PL3.

So for those of you who have been in this position before...what did you choose, what would you recommend, and what's your reasoning behind it?  I'm really not leaning toward either option at this point.  I had planned on getting an LX5 for nearly 2 years, then started giving the m43 a more serious consideration and had my mind made up on the E-PL3 for a few months...then realized that the LX7 was actually in that $3-400 range as well...so now I'm just trying to decide.