eBay and Craigslist finds

^ No photos/link, but if it's free then "yes" it's worth building up whatever it is, if only for the experience.

There is nothing wrong with lower grade tubesets (I'll warrant that few here could tell the difference in a blind test), the point is that there is so much 531 about that there is little point in paying for less.

This is especially so, as the difference in cost is minimal on account of all the chancers flogging conversions that they think are worth the sum of their parts.

Exactly. I wasn't trying to sound snobby! At least with 531 you know you're probably getting something fairly well made. Though I suppose the same could be said for 501.

Whenever someone asks me what to look for when buying a used bike I'll usually say 'go for 531 at least' as that seems to be a general guideline for getting something that isn't total bullshit.

Needless to say, I would never, ever advise someone to buy a conversion from eBay - these are rarely worth the sum of their parts, whereas original road bikes are often worth more.