Just a quick note: from personal experience, I've been a lot more productive in Clojure than in Java, and I have written a lot of Java code. Things like the REPL, STM or FP speed you up a lot, I would say by a factor of at least 2 - 3, maybe more. I have no data to back it up but this is my perception.
So hiring one programmer instead of 3 and paying him 2x more is already good for you.
When I switched from C to Java, I experienced a considerable bump in development speed. Just the collections framework was a godsend, not to mention things like GC etc.
Quite literally I would write things in days instead of weeks. Same thing goes for Java -> Clojure. And just to be clear, it is not my favorite language.
My point is - are you sure you just aren't better programmer overall and attributing that (somewhat underservedly because GC and a huge choice of collections) to Java/Clojure/<insert language>?
C++ has stl with many of the same collections, and if you want to use auto_ptr, you don't even need to remember to call delete.
I am not saying there are not productivity gains to be had from using java, but as in this case, it typically comes from not having the relevant experience elsewhere.
From a quick glance at the docs glib looks good but it is still too low-level for normal app development (for example, the size of a hashing table created by hcreate() is fixed; so you have to create & copy & destroy a hash table if you want to add more elements than it can hold at a time) and it should be, that's the whole point.
C++ is a whole other story, sure.
Well, it's been known for awhile that languages and environments can have a 2X or 3X influence on programmer productivity.
http://www.qsm.com/resources/function-point-languages-table
However, it's also widely held that individual programmer ability and the cultures of certain groups can have even larger affects on productivity.
Switching languages is hard. Managing groups is hard. Dealing with the rest of a large organization is hard. If a group can do fine without switching languages, why would any manager be in a hurry to do it?
Lots of angles to consider not just in terms of monetary. Human's behaviour/attitude/mindset is a very large unknown despite however hard we tried to make a "human" as static as a "resource".
I would rather hire somebody really good for $6k / month than 3 people for $2k each.
There are lots of good reasons to have multiple developers on a project other than simply throughput.
But alas, finding the ideal situation is like winning the NBA Championship trophy: you need all the stars to line up including "Lucky" star.
Personally speaking, even though I really wanted to love Clojure, I was forced to conclude that Python is more productive.
In my experience, though, metaprogramming is of limited use as anything other than syntactic sugar. And it often leads to very confusing code.
Other language features are far more fundamental and important: libraries, good integration with the shell, coherent error messages (!), readability, tooling, deployment, etc. As a language Clojure is beautiful, but as an ecosystem it has very far to go.
In my experience, metaprogramming is a wonderfully powerful utility for controlling complexity and confusion.
As far as the ecosystem - I used Python for a couple years, it's good. But the Clojure ecosystem is doing pretty darn well itself these days.