I think 5600 is too short to cater for all. I also think its hard perhaps even impossible to please everyone. We just built a second 18 holer at 5500 yards, it has fans but it has an awful lot of people that dont want to play it because its not long enough. That aside I agree that 6000 par 70 is probably the best way to cater for as much as you can, it can test the good players and not too tough for lesser whackers.
The length of courses and championship standards etc etc is nothing to do with the current downturn. Excluding the current economic gloom, two big factors are against golf. THE TIME IT TAKES TO PLAY and THE COST TO BE A MEMBER. The more golfers that become nomadic will equate to them playing golf less and less, if you are a member you tend to pop up for 9 or just turn up on speck, these things are not so easy for nomadic play.
When the world recovers, golf courses will start in Eastern Europe where there are not many courses, there is some great land there too but they are likely to be low standard affairs for the locals who have SKY TV and have watched, liked and now want to play golf. I assume Cuba, South America and other places will be hot spots too.