Do you know the approx date IOR became less of an influence?
IOR declined following the '79 Fastnet disaster, where IOR-design extremes were indicted as less-than-seaworthy designs. At the same time, the overall sailing and sailboat racing market nosedived in the recession and luxury tax debacle. Some, fun, fast, one design, dinghy-inspired, sport boats like the J/24 and West Coast-style surfing boats introduced in the 70s shifted the sailboat racing market from the heavier racer/cruiser designs to planing sportboats with asymetrical spinnakers. IOR was replaced by IRC, then IMS, and now by PHRF mixed fleet and one design keel boat racing, like the J/105s.
The sensible, traditional, seaworthy, cabin layout you favor - v-berth, simple head and hanging locker in the foc'sle, full bulkhead, pilot berths, cabin berths, navigation table, and quarterberths is found only on racing boats, and has now given way to the condominium layout favored by the picnic sailors - open cabin with prominent dining area, swivel chairs, enclosed spacious aft head with shower, claustrophobic double berth under the cockpit, and if the boat is large enough, double or triple cabins, for all your closest friends and relatives - perfect for motorsailing to the next raft up.
So why do some of us still like the boats built in the 70s and 80s, "tired" as they may be?
...or see a late '60s racer/cruiser like a Cal 40 smoke the fleet in an ocean race?