I've never done a decoction. Now that that's out of the way, let me just say that I found it interesting in Brewing With Wheat, by Hieronymous, that some of the traditional weizen breweries in Bavaria tend to only do decoction mashes when the ingredients call for it (i.e., when using undermodified malt). I found the takeaway point to be that while brewers can manipulate the wort profile with decoction mashing (breaking down proteins via protein rest -- when necessary, increasing wort fermentability, etc.), there are not enough flavor benefits to justify performing a decoction mash for every batch. Of course, there are plenty of traditional weizen breweries who still seem to employ decoction mashing as a matter of course.