Where to start...Let's see...
Here's a good start...http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.1999.tb00020.x/pdf
There are so many reasons to do step mashing...
When I've read through articles & experiments that make comparisons, they are typically configured in such a way that they are inherently flawed & seem to be TRYING to disprove the practice.
When decoctions are used correctly, you can not only taste the results, but you can smell, see & feel the results.
A simple single infusion with melanoidin malt will never get you in the ballpark of a correctly-executed triple decoction mash.
It's just not chemically, or physically possible.
We can disagree about this, forever.
It's not going to change the nature of the enzymatic activity that takes place.
If you're brewing a 75% Rahr 2-row beer, that's heavily hopped, it's probably not going to benefit you.
If you're brewing a 90% Floor malted Bohemian Pilsner beer, you're going to notice the difference, without even trying.
If you're doing a festbier that's based on a high percentage of Vienna malt, you're going to notice.