I tried approaching this by thinking what I had 35 years ago that I wish I had now (excluding any nostalgia or 'vintage' attraction). I can't really think of anything that I had then that I'm not happier or as happy with the modern equivalent. I did like my old Suntour VGT rear changer but to be honest, I like my Tiagra rear changer too (and it is designed to handle a 9 speed cassette). I thought Mavic module E rims with Michelin Elan tyres were the bees knees but the modern stuff is better.
There is only one thing that I think I might have been happier with than the modern equivalent and that is a 'padded' insert for my cycling 'longs'. I don't know if my arris was a lot tougher then than it is now (and I only cycle relatively short distances now compared to then [up to 40mile compared to 100mile] - maybe that's the problem - if I cycled more, my arris might be better conditioned), but I've yet to find a modern padded cycling short that doesn't create as many problems as it solves - so much so, that I find it more comfortable to forego the padded cycling short and use seamless microfibre underpants and unpadded longs instead.
Back in the early eighties, I had a 'polar fleece' insert, that was purchased separately and then sewn into the longs/shorts of your choice. In those days I found it most comfortable and without problem and I wish I had a stock of them now.