I think a decoction mash can make a difference when all of the parameters of the mash are in order. Proper grain (under-modified), proper heating schedule, proper enzyme activity, etc... Pilsner Urquell has it down pat. However, they have been making this beer for decades and have refined their techniques.
Personally, I've found that a decoction mash makes great beer but so does a single infusion mash, supplemented with some specialty malts. The difference to me is not overwhelming, and I believe one can make a beer just as good using any mashing technique (single infusion, step mash, decoction mash) by tweaking the grain bill and mash schedule.
That being said, I recommend trying it (decoction mash) out for yourself. The only way to really understand the effects of a decoction mash is to try it for yourself and compare it side-by-side, via blind tasting, with a single infusion or step mashed beer.