I think this is a big misconception of many. The benefits of critiquing the mixes of others is just as much about the person doing the critiquing as it is the person posting the mix(es). There is SO much to be gained by listening to other's work and analyzing what they've done. You'd be surprised at what you'll pick up on in a really short period of time.
The big deal about it is that it gets us to listen in a way that we don't with our own material. Our tendency is tune out things in our own mixes, whether we realize it or not. Listening to other's work, we tend to be more objective. We notice things that we ignore in our own work.
I've personally picked up a number of great ideas to apply to my own work from listening to others. Editing tricks, effects tricks. Tons of stuff! Regardless of your level of ability, you are a fan of music. You KNOW how to listen to music. You know what you like or dislike. Even if you don't know the "fix" for certain things, you know if something sounds off. You even know how to describe it. Compare those mixes to the pro stuff. It's a great way to learn your how your monitors work too.
Just dive in! You'll be surprised at how quickly things start progressing once you do it!