From what price would you say speakers hit the point of diminishing returns?
Diminishing returns obeys a 'general rule' that makes the most expensive products of each type unlikely to deliver value for money. In a technology area, such as hifi, there are definable parameters of performance with measurable standards of excellence. And what invariably happens, is that refinement over the years leads to a lot of performance being achievable at a modest cost, and usually sold at a price level described as "good entry level". When we compare the performance rating of this gear to the price, we get a peak value-for-money rating. To increase the performance rating by 10% will require a price increase of more than 10%.
From that point onward the incentive for spending more is no longer value for money, it is willingness to pay. There are performance gains to be had, for sure, but only at a diminishing return per dollar.
How low-priced is this peak in value for money? Usually pretty low, for a refined technology. Which should be good news for those interested, but for some reason, enthusiasts can get cranky about it.
If I had to guess where it might be for in-room hifi, I might point to a $700-1000 subwoofer with auto EQ like Elac Debut SUB3030 or SVS PB/SB-1000/2000 Pro; controlled-dispersion flat-response powered satellites like JBL LSR 305/308 II for $300-500; and a digital multi-source music player for $400-500.
cheers