old vs new

You are making sense, but to take advantage of this realization, you need to do a hell of a lot of research.

After which you will find that the truly great older items (as good as or better than the new stuff for half the price?) are just not coming up for sale because people hang on to them forever almost ;--) I waited two years for a Levinson 25s phono preamp and paid about 20% more than I should have -- but I just didn't want to wait another two years! It was worth it though because now it matches my 26s preamp, AND, we must remember it cost 7K 10 years ago and I only paid 2.8K for something that would cost at least 10-12K to duplicate with a new product today.
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Thats what I thought. My cousins 20yr old maggies sound so much better than some of the 'expensive' new stuff i'v heard.

Interesting question and no easy answer I think. I always buy 2nd hand but not 5 to 10 years old. Most boxes loose 1/3 of their value leaving the shop, so you still get great value nearly new. I was discussing this with a UK dealer I really respect and he says he despairs that nowone listens to his advice and that some kit has come on leaps and bounds in the last few years. For example, the Unison Research Pre amp he feels at about £1400, is as good as £4000 units a few years ago.
To answer your question, go for in demand kit less than 2 years old, you should be able to resell at mimimal loss. For example, I bought a Lavardin IT a year ago which is still worth what I paid for it. The great advantage is low risk, buy new and if it is a mistake, you have made a big loss, 2 years old, minmal loss.

Well today is your lucky day, I owned all the pieces in your examples.. #1 SFL-1 was my least favorite tube preamp. I say look elsewhere, yes there are some newer units from small U.S. manufactures and other used units that are better in my opinion.. The mcCormack, good amp, solid state sound, not bad on the used market for 600 or so. Odyssey, is a better amp with higher quality parts from my experiance, sound is somewhat similar depending on what you feed it with preamp wise.. However WAY more power and control from the Odyssey. It is a super solid design, build quality is as simple and hiend as it gets realistically. But truth is a new Odyssey is still double the price of a used mcCormack so its a toss up. Try a used McCormack for cheap, and buy an odyssey on the 30 day trial, decide for yourself.. Worst case you either return the odyssey with a loss in shiping, or you sell the mcCormack for the same you paid. By the way, none of these or newer stuff has much of a Newer technology, but with a newer piece you will get more than likely better capacitors made today then were made 10 years ago, and they will last longer, but this is another thing that goes back to the odyssey thing, you will get a full 20 year warranty anyway.

So at the 1000.00 dollar mark, there are very good new items as are used.. At higher prices at lets say 2 k plus you then start to set apart New vs. Better stuff used. Specifically pertaining to the odyssey's, they are as good and use just as quality of parts as any Levinson, Pass, Krell etc.. In the 5 to 6 k range anyway.. They are the best A-B amp values today. You can find many reviews on all 3 of these items in the hundreds.