I've thought on this topic quite a bit since moving to Europe for this tour. Several of my nicest rigs are in long term storage, including a Chesini I left in prepped form for a future build up (thread to come in..oh 2014 or so), but I couldn't help myself when I saw a '78 'Nago for sale. I paid way too much for it, but it is a gorgeous bike, and was fairly ready to ride, and I needed a L'Eroica rig for this year (I hope).
After much thought I have come to believe I am about done with the amassing bikes phase, and am just going to enjoy the riding and tinkering with what I have from here in. Granted, with some 9 bikes in all (or is it 10?) that's hardly a sacrifice. I just think the "find it fairly cheap and resto yourself" within a reasonable budget days are gone for me. My first real resto was just in 2008, a $200 complete Raleigh Comp GS that just needed some love and a few reconditioning parts. I don't think I put more than $600 total in it, and I doubt I'd be able to come close to that nowadays. It's been an uphill climb in expense ever since, but I am just happy to have the bikes I really wanted to find before the prices shot up.
I doubt it will stay this way though. I think (hope?) we've seen the peak in Campy value, people selling SR pedal dustcaps for $100 (saw that bid close a month back), and the rest. I think the vintage appreciation will run its' course and the costs will start to go down, although probably not to pre-2005 levels.
Still, all in all, to get a very nice condition 1978 Colnago for only a couple hundred over what it cost when new? Not bad considering inflation. I sure do enjoy the hell out of riding them, and messing about with the parts almost as much. It's a great hobby we've got here, doesn't hurt anyone, and keeps us all wrenching or riding and out of our wive's hair. I'm really looking forward to the next 20 years of it, e-bay be damned.