I'm working on new and older bikes every day. One thing that strikes me with bikes that I remembered as being amazing only a few years ago is just how damned heavy they are. They also all came as standard with long stems, narrow bars, often crappy tires etc. So you'd be upgrading it before it even went out of the shop. These days you can buy something like a 'low' end Norco Sight which comes with a 1x11 drivetrain, dropper post, wide bar, short stem, Minnions, up to date geometry etc for a lot less than the 5 grand quoted for a top spec'ed bike from a few years ago. The new bike will run rings around an older high end bike in every respect.
Sure, the boutique builds are priced a bit 'out there' but you really don't have to buy them when you can get a really good bike for a lot less. Obviously though, the bling bikes are going to be better still if you have the cash but it's the law of diminishing returns as you spend more money.
But the cost to produce the older out of date bike is really no different than today's modern rig. Handlebars few inches longer, frame tubes a few inches longer and a few degrees different angles are no justification for much higher costs. Dropping the front shifter should bring costs down not up. At least for mid range bikes.