Plenty of wise words and food for thought has flowed from this discussion. I'll chip in with my $0.015c australian ...
This is a very complex subject that is also at the very heart of our collective interest. I have enjoyed reading the varied responses and noting how consensus on the matter is hardly static or unified and just how difficult it is to define what constitutes restoration (renovation/fabrication etc).
I do have to question just how many bikes have failed or broken for lack of a repaint. Maybe call it the "just when is too late?" principle. If some reasonable measure for storage and maintenance was taken I have seen and experienced exactly 0% total failure of classic and vintage bikes that date back 30, 50 even 100 years. I'm sure there must be some failures out there but I think they are in fact very, very few and hardly enough to warrant such an obsession with renovating and repainting old frames. I have seen failures from bad manufacturing (overcooked, poorly brazed etc) but never a failure from being "too old". Conversely, I have seen irreparable damage by those who sought to restore/renovate. Sand blasting gone wrong, horror chrome jobs, UPS ate my frame stories and yes ... bad powdercoat (notice I said bad, there is such thing as good powdercoat).
I think that as a group we do tend to over-restore. We might say that we are the custodians, or keeping history alive etc etc but some of us have a habit of making bikes "ours" with fresh paint when they really didn't need it. Often they aren't significant or historic bikes .... just nice ones that we pined for in our youth or wished they were a different colour or wanted to look like new again. We're not alone ... Alfa Romeo's repainted in red or Jaguar's in BRG is a cliche that is common. Don't take this as a slight ... I think it's normal and human.
I don't think I sit in any one camp. I like it all ... from the bikes that look better than they did new to the bikes that not one thing has been changed and every single nick, scratch, bump, speck of dirt and grease is kept as a badge of honour reflecting years of use. The melange is fascinating and much of a bikes character and attraction largely depends on each bike. There aren't many rules. Provenance is something that I find truly outstanding and noteworthy ... few bikes could touch Michael Allison's Masi made for him by Faliero at Vigorelli. Stories like that are spine tingling. But most of all, nothing beats seeing an old bike being ridden. Ne plus ultra !!!!
Anyway's ... I'm rambling on and just wish to say "Let it be". There's many bikes out there and each of us probably own enough to rotate the miles or have newer bikes that get abused so that our keeper's remain. For the most they are ordinary production bikes with no significant history and there is no reason to get all "fashion makeover" on them. Use them, maintain them and they'll outlive us all. It's not a sin to let old bikes look like old bikes. I ask you to really think hard about how many bikes have crumbled beneath you if reasonably stored and maintained? I'm not saying no to restoration either. A gleaming perfect example is nice too ... just ask whether it really needs it.
You make the best soup with an old pot. I call it restoration to give it a wash, wrap new bar tape, re-lube the chain and repack the bearings and b/b.