What should I expect moving from MM to MC?

As mentioned, consider the Soundsmith Otello. Great cart for $400. The Audio Technica OC9 series are good value MC's.

Whatever cart you have, it will be limited by the phonostage.

Consider at some point a stand alone phonostage.

This will be "better" than the internal in the Denon.

Schiit Audio: Audio Products Designed and Built in California and Texas

Thank you both for the responses. The Denon amp is set up for MM only, but I read that I can use an MC High Output cart with no issues.

A few points/questions:

1. What I like about the Sumiko carts is their broader frequency range. The RP-500M's can reproduce frequencies up to 25khz. Some of the cartridges out there are limited at 20khz. While I've never been "tested", I have very sensitive ears and believe I can pick up frequencies over 20khz. So to this point the Otello may not make me happy but the  OC9 series looks like it would.

2. So to get to the bottom of it, for more warmth and fullness am I chasing the wrong animal in looking at a cartridge upgrade? Or would I be better served with separate pre amp and amp? or even speakers that may reproduce the mid range better/fuller?

Again, thank you. I am learning a lot here.

Many manufacturers publish frequency response data limited to the "audio bandwidth", which is generally taken to be 20 Hz to 20kHz.  However, nearly any good cartridge has an upper end response extending well past 20kHz.  The fact that one manufacturer publishes data out to 25kHz does not at all mean that another cartridge for which the data only show the response out to 20kHz is relatively bandwidth limited.  There are many cartridges (of all 3 types) that have response out to 40kHz or even 50kHz.  That's not a good basis for a priori judgment of "goodness". 

I agree with others who suggested Audio Technica or Soundsmith in lieu of Sumiko.  I have owned two high output Blue Points and found them unexciting compared to any of several very good MM or MI types. Not sure you have enough gain for the OC9 without either a SUT or a new phono stage.  Find out the actual gain of your built-in phono stage, in terms of db.  You'll need to know that if you want to consider mating it to a "high output" MC.  (I don't like high output MCs compared to the best MM, MI, or LOMC types.)

To answer your opening question: "What should I expect moving from MM to MC?" My answer is you would then appreciate the differences between the two particular cartridges; such a comparison of one vs the other would not yield information on which you could generalize between the two genres of cartridge, although some audiophiles do that.

@tablejockey I like the idea of the pre-amp. A friend of mine recommended this, as well. Do I then route the pre-amp into the Denon amp phono inputs? Or other?

Thank you @lewm . Your response makes sense. I am going to look into the pre-amp first with my current setup. From there I can dabble with the cartridge, if necessary. I'll look at both of the recommended ones.