I'm quite content that baits do "blow". However, what blow means to one angler might not be the same as it means to another. To me a blown bait does not mean that you'll never catch on it again, just that fish get progressively more wary. Potentially to the point that they become very difficult to catch on that bait. A period of the fish not being subjected to that bait may see it come round again in effectiveness. It's also a pointer as to why the angler that does something a bit different to the majority can have significant success.
I suspect that a highly scented/flavoured or unnaturally coloured bait is much more likely to "blow" quickly. I feel that the effectiveness of washed out boilies on pressured waters is reasonable evidence of such. Over the past few years, I've also witnessed a cyclical acceptance/rejection of certain baits. Fishing a fairly lightly pressured stillwater has been an education in this respect, though I make no claim to have it "sussed". It would be foolish to claim such as it changes subtley from year to year, sometimes for no greater reason than the vaguaries of the weather.
Around this time of year (Oct/Nov) the amount of folks fishing dwindles, along with the amount of bait going in. Come the following March, the carp seem to have all but forgotten what a boilie is. When the angling activity increases with the improved weather and temperatures, the odd fish falls to boilie, but not too many. I've had more success early in the spring fishing maggot in the margin after spotting signs of feeding fish. As the year rolls on, things get progressively more difficult. Margin feeding fish can still be found, but they become increasingly wary of beds of maggot. At worst, the introduction of a few maggots, in the middle of a coloured feeding patch, can see the area clear, yet it stays cloudy with obvious fish activity on either side. By May/June (ish) there has been a steady increase in boilie going in and the fish increasingly respond well to them. Before you know it, but hopefully after you've had some success, it's back to Oct/Nov and the cycle starts over.