I have an 'old' steel frame from 84 that I love, it fits me and works just fine as it is but I'm absolutely fed up of reaching down to shift one of my 12 gears ( Shimano 600 ), especially when riding in a group, so I'm going to buy carbon centaur and some new handbuilt wheels.
Personally it boils down to budget. I have about £800 to spend and for that money I'd rather have the centaur equipped 'old' frame over a low level otp modern racing bike and this also means that down the line, when the funds are there, I can updgrade my 'old' frame to something more modern ( I'd love a stainless Rourke ) and then rebuild the old frame with it's original parts.
I think the debate going on here is pretty pointless and it is all down to your own tastes. I myself love the look of old steel with a modern gruppo... modern materials may well be lighter and stiffer but honestly, am I going to be racing it? No. I just want a bike I am comfortable on over long distances, a bike that suits my abilities and ultimately a bike that I find aesthetically pleasing.
I love this: