Ben
I think your post is spot on and asks a very worthwhile question. But don't worry about things you can't control. We can't control how "other" folks will react. I've seen that time and time around this place. You make a simple observation about prices... and BANG!!! Somebody thinks you're "complaining". 
That's their problem -- not yours.
By and large,these product re-issue's thrive on INCREMENTAL improvements over prior versions. Seldom anything overly dramatic for sure. Sometimes it's smoother slow-speed control, or better sound (Legacy Railsounds is tops!). Other times it's little stuff like 4-chuffs per rev instead of 2.
But the improvements are enough to warrant interest that keeps prices at a premium for the new stuff. Consequently, prices of prior releases have nowhere to go but down. We're not in a collector's market anymore, so there's little to no "glory" in owning older versions of something -- even if they were produced in limited quantities. That's why the most successful dealers today move inventory... and they move it FAST.
I guarantee we'll see a day when even Lionel's die-cast ES44 diesels will be obsoleted by some feature on newer locomotives, and current owners won't be able to give those things away. May not be this year or next year, but that time will come. Count on it.
Although I hate to generalize by putting labels on things, the 2-rail culture is admittedly very different than the 3-rail culture. The 2-rail culture has its roots in more of a "modeling community" -- dare I even say "think HO or Model Railroader", whereas the 3-rail culture is more of a "ready-to-run crowd" -- GENERALLY speaking.
Now that's not to say 3-rail folks don't like to tinker... 'cause we have some of the best right here with GRJ and Alex M. I wouldn't hesitate a second to have either of these gents upgrade one of my prized locomotives. 
But as CW pointed out, upgrades are not always available in the 3-rail world... and the importers would much rather pump out product re-issues to generate new revenue. It's an ongoing cycle that we've seen time and time again, and 3-railers have been conditioned to the cyclical nature of product re-issues to the point that most are quite comfortable with it.
Having said all this... I do think that we're reaching new pricing levels nowadays that are gonna make it tougher for the same number of folks to keep buy the new stuff. Of course, some will... and that will keep the importers very happy for sure. But increasing numbers of toy train enthusiasts will also find contentment with the "n-1" or even "n-2" generation product. There are lots of ways to enjoy this hobby without necessarily having the latest and greatest.
David
