Leaving polemic aside, I think the point you are making is that for you investing this amount of money in a headphones amp is too much. Legitimate, understandable and probably widely shared.
Having said that I find debates such as “is it worth the money?” not very interesting, it is just too subjective. Listening impressions are always subjective, but they can be useful (and fun) to debate. When it comes to investment decisions the discussion quickly hits the wall…
Coming back to you point, and to move the discussion forward, I think that products such as the AIC-10 are “shocking” today because we have seen very few headphones’ amps at this price point (I can only recall Viva at the moment – another Italian amp!).
When the HD800 was launched in 2009 the price was a shocker. I also suspect that the range of top dedicated amps to make them shine was rather limited. Ten years later we (crazy HeadFiers) have come accept that companies can propose cans for 5 - 6k euros. Similarly, DAC specifically designed for headphones (e.g. Chord) also go for above 10k euros to no one surprise. Few amp companies are going in that direction at the moment and they are obviously raising some question marks.
Again, I am not interested in convincing anyone about the “worth” of Riviera, my point is rather than the headphones world, including amps, is catching up with a more consolidated trend in speakers hi fi. The offer is wider at all price levels and the very top we now have incredibly well designed, performing and expensive products.
Is that good or bad? I leave it up for discussion