I don't do these types of polls, but I'll chime in on the addons in question.
I've had Silver Wings (by Bill Lyons, google The Old Hangar) as an install for 50's era flying. All Calclassic AI - nary a jet airliner to be found, except for the Comet and Caravelle. Unlike Willie, I tossed out the stock jets and turbo props. There are enough packages out there to cover the entire earth reasonably well with piston engine, early turbo prop aircraft of that era.
I've also created another install, also using Silver Wings, that has the 70's era. That allows a slightly more modern environment for the rare instances where I want to fly a more "modern" aircraft - F-101B, F-4 Phantom, F-5 Tiger, etc. The process I'm describing below applies to either 50's, 60's, or 70's (or any era) - but since the focus seems to be on the 50's ....
The trick for me was to tackle it in two parts.
1. The stock traffic.bgl can be as much your friend in this situation as your enemy. I opened with TTools, and replaced the aircraft references with those airliners that I handle showing up randomly around the world. In my case, I replaced the Orbit 747 with the Pan-Am B377, the Soar 747 with the Transcanada Airlines L-049, etc. Replaced all of the planes down to the GA with Calclassic and/or stuff from Golden Wings and Golden Hawaii. That gives you lots of semi-realistic "volume" of AI. The key is to match the type of aircraft you're adding in as close as possible to the type you're removing. Hence replacing larger jet airliners with large prop liners, small commuters (Dash-8) with Convair 440, etc.
2. The realism comes from installing a good variety of the retroai airline packages. Again, I like to cover all the continents, major countries - and now you're really set. It takes time, but the combination of Calclassics and retroai allows you to cover the 40's to the 70's very beautifully - and realistically. I haven't seen an MD-80, 737, or Dash-8 in my sim in five years. Just for fun, I'll fly into some airport I've never been to, and see the airport full of airplanes from that country - that alone makes it worth binning all the stock AI planes forever - whether you want to go 50's or stay in the current time period. Flying into Vladivostok and seeing the airport full of Aeroflot Ilyushins and Antonovs is just too cool.
Of equal importance to the AI is the airports - and the packages from CalClassics and Early Sixties (avsim) are must haves. The latter is nice, because there's more flying space out there than just the USA - and that's their specialty. Airports in Karachi, Calcutta, London, Paris, Entebbe, Sydney, and dozens more are rendered beautifully, so at the end of the day, you can create an entire FS world that is scenery-wise and traffic wise, set anywhere within a 50 year period. The fact that you can do all this using freeware is staggering. Glass is definitely more than half full.
I hope this helps.
dl