I would no more pay a lot for a feeder rod than I would go on an expensive holiday, buy a flash car, or a £20 bottle of wine. They all have little value to me. However, I'm sure they will be worthwhile for someone. I also have little doubt that they are likely to be better somehow than their budget cousins.
Philip, I'll bet that there's something that you buy and value highly that would leave me as perplexed as you are by expensive fishing rods, it's just the way of the world. The one thing that does confuse me somewhat is why you aren't using £30-50 budget carbon. If there can't be any difference between your chosen (hypothetical?) £100 rod and a £375 rod, why is there any difference between a £50 rod and a £100 one? A carbon blank, some rod rings, whippings and a handle....so just like any other rod.