cj,  I agree about using any microphone won't work as expected.  So... I got curious about the 'Room EQ Wizard' and started reading the documents on it.

It 'appears' (since I've not tried it - but logically it makes some sense) to use nothing but a SPL meter.  It generates the spectrum - after calibrating the soundcard itself by using a loopback (which even the basic pro-sumer' should be pretty flat), it generates tones up and down the spectrum and measures the levels of each and records the spl along the way.  Admittedly, that is less than perfect but, could yield some real overall room correction - at least at any on given place in the room (the desk position, etc.) .  I would assume that is something like the ARC system does. 
 
edit: fwiw, if nothing else, the online help files for that piece of software is a good read on acoustics - the why and how an eq correction only, won't work and the room has to be treated.   We all know this, but tend think technology will save us

Something like that may have some value for someone just starting out or lacking in the funds for the real mccoy.

On a side note, I recall that Rane used to make and analyzer (no idea if they still do).  Back in the day (ha!) it was a godsend to come into a club you've never been in, hit that up, take some measurement and match up the final 'room' eq (last in my live signal chain) and in about 2-3 minutes, have some sense that the group you were mixing for would sound pretty much the same anywhere they went.  (I used to write all that information down on notepads (31 band eq's), then came along EQ's where you could store the curves - yay!)

Overall, I agree with you and the others and to the OP - the room and speakers are the key.

oh, and a few beers, lots of time to train your ears and an occassional pizza or two in those late night sessions and the very biggest thing (imo), working with others so that one doesn't get narrowminded in what they think sounds good.

Best!