I think purchasing power is an enormous factor in the hobby's development. We are far wealthier now than 30yrs ago (despite what some would like to believe).
We have more money spend on model trains. Model trains are cheaper than in the past, so we can buy both more and better quality (you can search for the thread in which squidbait pulled up statistics showing that a Bowser K-11 costs 30% of what it costs in 1955 or something like that). We also have larger homes...which means larger basements/attics...in which to build our empires.
I plan my model railroad on the space available...I presume others do the same. With a massive layout to work on...and plenty of nice affordable (not to me), RTR models, I suspect that people are spending more time performing basic construction (and hiring help) than building craftsman kits.
In the past, their were two types of people whom built craftsman kits: those whom wanted highly detailed models and those whom enjoyed the craftsman kits. Now, even a minority scale like On3 can be 100% RTR...so only those whom enjoy craftsman kits or can't afford a custom builder will build these kits. Beautiful models are no longer limited to those of us whom can assemble an intricate kit...I think that is great progess. With craftsman kits being limited to the sales of those of us whom either really like the construction or the prototype, there is a smaller market for them.
It sure seems like there has also be a noticeable shift towards steam modeling since the mid-'90s...with the shift occuring after Bachmann introduced their spectrum 2-8-0. They were $70 from the discount stores in 2000...and they are $70 at trainworld today (which means that the real price has dropped)...unless you get the dcc & sound version which didn't exist in '00. The 2-8-0 was a huge breakthrough in running characteristics, detail, genericness, and for a lower price the many of the existing models...the HMS Dreadnought of model trains. Certainly a huge leap forward for the hobby.
In summery, I believe that as our purchasing power has increased...we have chosen to buy larger homes, large model railroads, and large rosters. With less time available per boxcar...and a greater variety of equipment available stock...modelers aren't as interested in some of the now unessecary steps to create highly detailed empire.
I'm glad that I'm scratch building today and not 30 years ago. There are more detail parts available and some amazing tools that were impossible back then. Further, more research is available now than ever before for railroads such as the DSP&P...far, far more. People tend to forget that some supplies, such as readily available scribed styrene didn't exist 30 years ago. Resin has come a long way as well. I definitely wouldn't trade laser cutting, hydrocal, dcc, and scribed styrene for reading camelback kits, metal boxcar kits, and tools I can find on ebay.
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Some links if you doubt my premise of our increased wealth...median income, home size, national debt, unemployment...
http://mjperry.blogspot.com/2008/08/adjusted-for-household-size-real-income.html
http://upload.wikimedia.org/wikipedia/en/6/6f/US_Real_Median_household_Income.PNG
http://www.infoplease.com/askeds/us-home-size.html
http://en.wikipedia.org/wiki/List_of_countries_by_public_debt
https://www.cia.gov/library/publications/the-world-factbook/rankorder/2129rank.html
http://www.miseryindex.us/URbyyear.asp