I trained on steam without GPS, flying cross-countries with a watch, sectional, and E6-B. I've flown basic VFR steam and Skyview in the same airplane; most of the hours on steam. And I've found that other than a slight edge to a round airspeed or altitude gauge, glass wins hands-down everywhere else once you depart from day VFR around the patch. The biggest difficulty I had in adjusting to the Skyview was relearning my speeds (the steam was marked in MPH and the Skyview was in knots).
With glass I spend less time heads-down dicking with calculations and trying to read a map and juggling paperwork and looking up to make big corrections. I spend more time looking out the canopy, with a better sense of where I am (and where everyone else is), what's ahead of me, and what the airplane is doing. I can
see information (e.g. weather) instead of having to hear it from FSS and try to picture it in my head and cross-correlate it with a small map. I don't have to spend as much brainpower on low-level computational and administrative tasks, freeing me to focus on higher-level tasks. Especially with even a basic autopilot, I'm not nearly as fatigued at the end of a long flight.
To be fair, a large chunk of this capability can be had with an iPad, Foreflight, and ADS-B In, and most of it I don't really use when I'm making that day VFR local fun flight--just I keep the map pulled up so I can keep clear of the Class B and glance at it for traffic. But it really earns its keep on the longer flights.
Relevant story: So one day (2012 ish) my parents were flying up the east coast to go visit some friends from my dad's Navy days. They ran into some weather about the time they got to Virginia. At the time, Dad's airplane was in the basic VFR steam configuration mentioned earlier, plus a Garmin 195 (monochrome handheld GPS). Mom (not a pilot) wound up doing the flying while Dad tried to navigate them out of the weather and get them to somewhere they could land. Once they did, Mom turned to him and said "I don't care what it costs, you upgrade that panel or I'm not flying anywhere with you ever again". She'd seen what was available in other guys' airplanes, and even though she wasn't a pilot she could immediately appreciate the usefulness it could bring even to her.
Acclimation and aesthetics. Just like the first digital clocks and watches. A lot has to do with where you enter and where you have to go with the technology.
As I said, I trained in the all-steam no-GPS world. But my first professional job had me testing (what was at the time) the most advanced cockpit in the civilian world, in the engineering sim. I'd seen representations of early glass cockpits (1980s era, think MD-88 and 757 level) in my computer flight sims and my visit to the sim at Dad's employer, but I was utterly blown away the first time I sat in our engineering sim as a new co-op. Full-color moving map with a cursor and weather overlay?! And then they showed me the early alpha version of what would come to be called "synthetic vision". What was this magic?!
Now Dad's little homebuilt has that (and more!) on a strikingly-similar-looking display.
We're very near the point now where a basic EFIS and engine monitor package is cost-competitive to good VFR steam (I think we've passed it for IFR already). I think we're at (or even past) the point where it's lighter and easier to install. Now that STCs are out there to put experimental EFIS into certified airplanes, I expect that the market for round gauges, especially gyros and vacuum equipment, will dry up.
