There is no definite amount, but usually I have about 15 - 30 layers.

even in my most complex stuff I only end up with less than 30 layers. And the "muddiness" that you're experiencing might just be from the sheer number of sounds that you include in your track.

Not trying to sound like a dick but does it really matter?

Less = more.

The less, the better. Use your ears and see for yourself.

During the course of making the track, I probably have 30 or more layers, but I end up muting/deleting the vast majority of them by the end.

I usually end up with a group called "Floor" which is where I throw layers that I'm not ready to throw away, but not actually using any more.

Thats a bold statement haha. It really depends on how much detail you add. I've had tracks where my drum bus alone was like 25 layers (with percussion etc). Most of my tracks tend to have 80/100 channels, depending on how many arps, leads, chords and other instruments i use.

Sounds like my photoshop files.  heh

My song are finished when there isn't anything left that can be deleted. 

For starters it will have some dependence on the style you are making.  Like everything else in production, there is no right answer, but if you are consistently pushing 50 tracks, you probably need to do some cleaning up and organising your work better.  EG, you tend to get lots of one-off effects like swooshes etc on their own track, each with a reverb.  Instead, send them all to a bus with a single reverb, then flatten those layers together into a single track.  Saves a lot of confusion later.

You have to be organised from the very beginning otherwise you will find yourself in all sorts of trouble towards the "end" of a project

That Madeon screen cap, lol

I usually go for about eleventy layers, sometimes eleventy and a half