Hoping to make a huge MMO that everybody will love is ridiculous, of course.
But.
I wouldn't say give it up. I'd say take it in perspective. There's a lot of code that goes in to an MMO, and you'll need a really good coder to do it. When you have a coder, then they have to do what? Networking, animation, lighting, water, physics, terrain, objects, particle effects, AI, a terrain editor and probably a lot more stuff before you can start adding content. Keep up design for the MMO, just as a second priority to games which you can throw together to build up a code base for all of the necessaries. For example( off the top of my head ) a 3d tetris clone that uses cool lighting. Making that would mean practice with lighting, 3d, input. That's good. Then, when you think you have the code/experience to tackle an MMO, make it small! seriously start with one guy running around on a field with music in the background. This is assuming you've got a modeler by that point and a composer. Build from there. For a start, probably you only want one town with a surrounding field. See how long that takes you, make it fun within itself, and then you'll have something to show.
Just my take. I'm sure I'll be yelled at. I think it's more appealing than "make tetris forever" - at least you're getting a little more done. Of course, if you have trouble with making games to utilize MMO code, then you've got a long way to go.
