MCM was my first and one of my favorites (did it the year after Oprah, like a LOT of people). I lived there, but moved a few years later and have gone back and run it several times since then. Some of the luster wore off for a few reasons:
1) More competition from other races targeting first timers (here in Cincinnati the Flying Pig directly targets rookies), and a lot more competition in the fall in general - Chicago, Columbus, NYC, Twin Cities, Philly are all fantastic races.
2) Changes in the course - Crystal City is kind of a crappy part of the race - and it feels a little more disconnected from the monuments than it used to be. I recall in the early years running right next to the Reflecting Pool by the Lincoln Memorial, and now you're on the roads a little bit removed. I'd have to study it a bit more but I seem to recall enjoying the old course more than the last few times I did it. Part of that may be the crowd support mentioned previously.
3) Some logistics challenges with enhanced security measures. A few times, I've stood in a LONG line to go through a metal detector. That may be a necessary evil, but it does seem to make pre-race less fun.
It bums me out as I think MCM should be a must-do event for any avid marathoner (regardless of your politics!). October in DC is usually beautiful, monuments are great, and the Marines do a great job in supporting the race. There is just so much more competition in the fall than there was back in the 90's when I first started running marathons. I don't think trying to attract elites is the way to go - they should offer some prize money, yes, but I don't see how that would attract big numbers of people, and the top tier talent will find a faster course to race in the same time window. MCM has a niche to it, and they should try to exploit what makes them different.