I think the key phrase missing from all of these posts is CYCLES.
Every designed (ie. non organic) item that moves has a number of cycles that it is expected to undergo during it's life time. Your car door handle, the switch on your kettle and, yes indeed, the frame of your bicycle. All these are expected to last a certain number of 'moves' before they enter unknown teritory and probably break.
The designed life of a frame is say 1,000,000 cycles. (aluminum degrades an infintessimaly small amount each time)
Say my Pace RC-200 was NOS. It had a design life of 1,000,000 cycles BUT it has been on LBS wall for 16 years. This was never factored in in the design process and therefore cannot be allowed for. A prudent approach would be to HALVE the number of cycles that that frame can undertake safely before replacing it. (if it was an aeroplane wing spar this is what would happen).
So aluminum does degrade over time. But only so much. I think that too much 'worry' is generated over aluminium, I would be as concerned about the internal corrosion that may or may not have occured inside my Orange frame, or the condition of the epxoy bonding on my Dyna Tech as be concerned about my well used Pace RC-200.
The US airforce are cannabalising B-52 Stratofortress's (mainly B-52D's) that are mothballed in the desert to keep the last 458 B-52H and B-52G's flying. Some interesting facts:
The LAST Boeing B-52 built was an H model in 1967.
The B-52 has new replacement wing spars and skins at 350,000 Cycles (this is measured by stress guages in the wing) but many of the aircraft's stuctural members are original.
EVERY B-52D saw action in Vietnam and none were built later than 1962. These aircraft have useable parts on them today.
Yes aluminium degrades over time, but seriously what is the worst that can happen? Gravel rash? The USAF haven't lost a B-52 since the '70's for ANY REASON!
*The reason I chose the B-52 to illustrate my point is:
It is made almost entirely of aluminium and built with '50's technology. They are all very very old and they have had a serious amount of research done into their future viability by folks far smarter than I! What the USAF do with the B-52 amazes me, just think, every one is older than it's pilot now!
**The US Dept. of Defense (which just retired the F-14 Tomcat) wants to keep the B-52 flying until 2047
as the cost to design and build a replacement is unthinkable now.
Sorry this got a bit long-winded, I'll go and lie down now
Somerset, like 'Heartbeat' with newer cars!
Retro MTB: 1992 Cannondale 3.0 Deore XT M730. 1992 Marin Pine Mountain Deore DX M650.
Retro road: 1992 Eddy Merckx Corsa Extra Telekom Shimano 600 STI. 1993 Dyna Tech Ti.
Modern: 2006 Wilier scandium Ultegra 6600. 2014 Wilier GTR Ultegra 6800.