I seem to recall somebody did a side by side comparison of a beer with a decoction mash and a step mash with melanoidin malt and had a bunch of people judge the beer and people noticed a difference but thought the melanoidin malt beer was smoother and more pleasant. I seem to think Nateo posted it on his blog a long time ago but I haven't seen him around these parts in a while.
Outside of maybe making more starches easily available for conversion, I'm not a huge believer that decoction mashes offer a lot that a step mash doesn't but there is probably a subtle difference. I imagine very long boils on the decoction probably makes more of a difference but a 10-15 minute boil probably isn't creating as many flavor compounds. I do know some pro brewers swear by decoction mashes when using undermodified malt. I can see the need for the decoctions to help with conversion.
Since I don't have mash tuns that sit on burners I have to do my step mashes by decoction or infusion. I've never made a beer with a decoction mash I disliked but I also haven't found that magic touch either.
I have made a bopils with a double Hochkurz decoction and have made that same bopils with a temp controlled step mash at the same temps. No difference for my pallet and, frankly, I recall the latter to have been a better beer. That said, the helles that I did this quick and easy decoction on was a very fine beer and had some subtle nuances that the same beer with melenoiden malt just doesn't have (I'm not saying that melenoiden malt attributes flavors resembling decocted beers).
In my opinion, a traditional blood sweat and tears decoction isn't worth my effort. But the pressure cooker method is so easy that I may get a portable electric burner so I can do it right next to the brew rig on occasion. Even after 15 minutes, there was a noticeable aroma on the decocted grist that the rest of the mash just didn't have.