I don't quite understand why people think that modern bikes will all be landfill with steel ones still going. I agree that crashes will take their toll on carbon frames, along with integrated headsets (yuk) but modern Alu bikes seem to have got over the teething troubles of early years.
I wouldnt fully disagree re the alu frames. However, modern wheels, bars, stems & groupsets are built for weight reduction and/or performance only. If anyone talks of durability, then theyre either old fashioned or a skinflint. So, ergos/sti's have plastic workings with limited life, youve mentioned the headsets, external BB bearings have short lifespans, need i go on. I still have the stuff from my racing days in the 80's which were until very recently on a winter bike. The stuff has now been removed and will form the basis of a "back in the day" racing bike. It all still works. Would be interesting to see if a modern racing groupset would function well in 25 yrs??
The problem with buying an older bike is the combination of 27" wheels, freewheel hubs, 126mm spacing etc etc. While it's all upgradable, it does cost a lot to do so. Bearing in mind the OP said he doesn't know much about bikes, and is trying to get something to commute on, it's a bit of a minefield to start. Plus, take it to any bike shop and they'll say it's cheaper to buy a replacement (and they'd be right).
I agree that a 1985 Dawes Galaxy is in many ways nicer than its modern equivalent, but it would take time and fiddling to bring it up to scratch for everyday commuting...
depends how old. A mid 80's bike onwards, would have a freehub (albeit 7 cogs - and theyre readily available) and 700C wheels
I wholehartedly agree with modern is probably cheaper and much easier, esp for someone without the knowhow. Retrobike traders have now pushed parts prices towards new stuff. My new winterbike is now all modern shimano cos its widely available and not much more costly than specific retro parts. However, it performs like a racing bike with guards. I wouldnt want to use it as an everyday commuter - I'd take the weight and want something a bit more bombproof.
I feel that for the future, I will have left retro projects alone, to go with the flow of modern stuff and retro will likely be something I appreciate, but not partake in. A pity.