Well I don't have empirical data to back me up but I don't see how developing provinces is better.
One development will give 250 troops in that province and then is further improved by whatever bonuses you have lying around. Assuming the average cost for development is 60, you can get roughly 1665 troops per province for every idea group (400 points). Sure, it stacks with building bonuses and percentage bonuses, but a lot of the ideas seem stronger.
Just the opener of quantity gives you a bonus of +50% which returns a lot more. The recovery speed also helps a great deal, because it doesn't matter if you have 2000000 manpower or 10000 manpower, as long as it doesn't hit 0 you are fine. And at the end you get +50% Land force limit modifier, holy crap that's a lot!
Same goes for most other idea groups. Any group that gives +5% discipline is already worth it. Stack that stuff up and you get an army of immortals.
If what you say is true, about the general consensus being that ideas aren't worth it. Well I say they aren't seeing the whole picture. The idea's on their own might not be god tier, but when combined just right you can turn into a behemoth.
Offensive + Quality + Economic + Quantity =
generals with a base of 2 pips and more tradition so your generals roll more pips afterwards
+10% to all troops strength, so your 50k army is actually a 55k army
+15% morale, fuck having a stronger army, even your smaller armies can route the enemy
and don't forget, your army is huge and inexpensive and these aren't even all the benefits
In the end you end up with a behemoth super army. Far more useful than just having more manpower lying around. Also because you wont be losing nearly as much troops.
But like I said, no actual empirical data to back me up. I might very well be wrong, but seeing how I rofl-stop every ironman game since the beginning.. yeah. (P.s. this is my first Iron-man campaign: http://imgur.com/a/t8qdx just having a super strong army allowed me to go this far in my first full run of the game.)