The road cycling population, in general, has not required a triple with your "granny gear."
That is changing, with many road bikes, especially entry level models, being sold as triples, trying to be all things to all people.
Also, compact cranksets are more and more becoming the option of choice for road riders in mid and even upper level offerings.
The riding population is also aging, and less able to mash it up grades. Either that, or people are finally getting realistic about riding hills.
Road bikes have long been based on what's being raced, and many grannies don't race.
However, if you're trying to sell a bike, there's no reason to exclude possible buyers who may need/want a little more climbing ability built into the bike.
Just as many triathletes try to buy speed, many riders want to buy climbing. You get what works for you.
For vintage bikes, the options as far as compact cranksets are limited, but I'd still go that way, or even just buy smaller rings up front and larger cogs at the rear. Going "triple" to add the granny gear can require many changes, some that could cost as much as your bike is worth. Best bet is a donor bike that can give you the shifter, crankset, bb, fd, and rd you may need.