I am a realism guy. I simply can not justify spending money on the old stuff that's looks unrealistic on tracks.
I see all kinds of MARX stuff on ebay in the road names I collect and I wish they would just have a separate subsection for that stuff because it fills up the categories I am looking at.
It appears realism is not important to you. I believe as others do that the old stuff can be fixed, and there is support for the old locomotives and rolling stock.
I would vote for newer. I run conventional so I use an MTH Z4000 transformer and have 2 tracks plus accessories. Obviously older stuff is conventional.
If you were considering older stuff to avoid the modern electronics, then I would not consider that as a factor in purchasing.
The oldest stuff I have is some single can motor Lionels from I believe late 1990's and they are junk, for me. Of course I could do a deep dive into why they don't work well, but to me I want dual motors and performance after the visual is satisfied.
Modern era locomotives, even some with sketchy electronics like MTH PS 1, look so much more authentic then 1950's to 1960's. In my opinion.
I would consider - if this is a long term obsession like my hobby in which I spend about $2000 a month on locomotives and rolling stock, and for which I am tapping down on my purchases after stockpiling about $20,000 worth of equipment, or if you just want to play and run 2-3 trains.
If I were to decide tomorrow that I wanted the old stuff, then I am stuck in a multi month ebay sell down and won't derive all of my value back.
That's probably more analysis than what you were looking for, but I thought I would comment for you and others.