"...steam is too expensive...everything is diesel..."
Well, as one nice steamer costs about as much as, say, 2 nice diesels, just skip your next 2 diesel purchases and buy that big Pacific that you want...same outlay.
========
Anyway:
It (low used-equipment prices) does lower my New purchases - except when it doesn't. If the loco is truly new (like the Lionel USRA Heavy Mike) I will simply pre-order it. I got my Heavy Mike, and it's nice, and I will be able to find it later at a lower price, I'm sure, but when, I don't know, so I don't care. Also, I helped make sure that it was actually produced.
If the item is important enough to me I'll just get it. Things like the always-expensive Lionel scale Mogul I did not pre-order, though I wanted it. With TMCC, but even the Conventional ones were high. Actually, the Mogul price was not too high, if you passionately wanted it - but for me, it was a desirable but "second-string" piece.
(This also demonstrates one reason that we don't have more nice, small, scale steamers - they cost as much to develop as a Hudson, as much to market, and nearly as much to build, but the customers won't spend as much - it's "only a 2-6-0".)
Then, last week, on Mr Bay, I offered on and won a NYC (which I wanted - it's close to a NYC 2-6-0 look) - with TMCC - for well under $400 (s/h was a tad high, though). So, in that case, I waited. (The Mogul runs well, BTW.)
Nice second-hand and earlier-production items are inevitably going to bring new sales down - how could they not? My concern is - and it's happening, already - that new designs and models of new prototypes are getting more and more rare. There are things that will never be modeled that would have been viable 5 or 10 years ago, but, among other factors, the "nice; Mint; NIB" and the like stuff is just too low-priced, now.
I'm seeing things on Mr Bay that I can't believe.