In terms of sheer aesthetic appeal, the DC-3/C-47 is at the top of my "most beautiful airplanes ever" list. It's just such an elegant, clean design; like the Platonic ideal of an aircraft.
On the other hand, my father had some occasion to spend time traveling various places in C-47s during his time with the Air Force, and he describes it as a bone-shaking experience. So maybe beauty isn't everything it's cracked up to be :-D
My first flight was in a DC-3, 1953, age 4. Philly to Cleveland, crossing the Appalachians at the low cruising altitude that they made was maybe not bone-crushing, but it was bumpy. The only time I ever got to use the vomit bag.
And here I was about to claim seniority. Mine was probably 1956 or 1957, Buffalo to Washington. I would have been at most 2, so I have no recollection.
I actually saw a turboprop DC-3 on the taxiway at Dulles Airport a few years back, while I was waiting around to catch a flight in a much more boring plane. It looked brand new, all gleaming metal and fresh paint. A beautiful sight!
I saw one for sale on Controller recently that was in spotless condition done up in Pan Am colors for barely under a million. Though the maintenance costs on that beast and hourly operating costs would eat you alive.
https://www.controller.com/listings/aircraft/for-sale/220858...
It's a workhorse and as much as I miss the thunder of the radial engines it's nice to see them get a new life. I doubt the C-54 will get the same treatment but that would be impressive.
There are vast logistics improvements to be had by replacing the old Twin Wasp radials with modern turbines.
Jet fuel is more common in airports than avgas, especially in a military context (this is why all NATO vehicles, including land vehicles, use diesel/jet fuel).
Spare engines and parts are a lot easier to find too. The PT6 turbine is still in production and widely used. The Twin Wasp radial hasn't been manufactured in decades, and I'm unsure if P&W still makes spare parts for it. There are less and less of them in existence every day.
Lastly, finding engineers with the required skills and experience to work on turbine engines is a lot easier than finding them for large radial engines.
I once had a beer with a RAAF engineer who used to maintain the old Caribou transports. He'd been doing it for so long he said he could remember the catalog part numbers of almost every engine component off the top of his head.
He said maintenance on those huge radial engines (The Caribou uses pretty much the same engines as the old DC-3s) was phenomenally time consuming and expensive, and spare parts are increasingly harder to find.
In addition to the reliability mentioned, the surplus power is important for runway takeoff performance and safety (carrying more weight off a given length runway and, in the event of a single engine failure, you want the plane to be able to climb away on one and large power surplus at low altitude is the answer). Turbines also have much more predictable service schedules, with fewer unplanned maintenance events.
Most turboprops also offer beta and reverse, which aids in stopping the airplane, contributing to both landing and rejected takeoff safety improvements.
Lastly, turbines burn Jet-A, which contains no tetraethyl lead, unlike 100LL avgas. Jet-A is typically more plentiful and cheaper per Joule as well, offsetting some of the fuel economy in gallons penalty. (The fuel economy in dollars is less unfavorable.)
There's a reasonable argument to be made that if the practical turbine were invented first, we might not have piston-powered aircraft.
While safety and emissions are nice side benefits I doubt the owners care much about that in this context. They almost certainly did it because consumables and spare parts for the wasp are drying up and for a flying aircraft you kind of need those things.
On the other hand, my father had some occasion to spend time traveling various places in C-47s during his time with the Air Force, and he describes it as a bone-shaking experience. So maybe beauty isn't everything it's cracked up to be :-D