Just to add to what others have said....
The efficiency of production is not the same as the efficiency of reception. A very short message with no redundancy may be easier to produce, but will require greater concentration by the listener. This is one of the tensions experienced by all languages.
Language is not just about the conveying of propositions. We also convey all sorts of social meaning in our speech, including about our own identity and our relationship to and attitude towards those with whom we are speaking.
Anthea Fraser Gupta
Let me refer you to an article by Dan Slobin that may address your question:
Slobin talks explicitly (as do others, but I find this article quite accessible) about countervailing linguistic pressures for what you might call efficient and inefficiency. You may need to increase redundancy (inefficiency) in a noisy environment, for example.
Susan D Fischer
As both colleagues have indicated, there are multiple components in linguistics at work can cause different effects. To take some examples
From phonology - the field of Optimality Theory explicitly claims that forms are optimized to best fit the priorities a language assigns to a number of constraints.
Some languages may have only 3 phonemic vowels because these vowels are the most divergent and most easily perceived. Others may have 10+ vowels which allow for more combinations of sounds, but at the price of more potential for confusion.
In fact sound patterns may change to make one part of the language less complex, yet it complicates another.
In the field of pragmatics, if you want to make or deny a request, the most concise forms might be something like this in a fast food restaurant.
"Give me some fries"
"No" or listener gives fries.
However, most languages use "politeness strategies" to make requests while not straining social ties. Hence, a more typical pattern would be the longer one below (especially in small towns where social ties are stronger).
"Hello - I would like some fries please"
"I'm sorry we don't have any ready"... OR "Here you are sir. Have a pleasant day"
"Thank you - Have a good one yourself"
To conclude, I would say that although efficiency can be seen as a linguistic factor, it is not a simple factor by any means. It will probably not result in "simpler languages" unless some other biological factor occurs.
Elizabeth J Pyatt
It's a good question, and yes, there are linguists who have discussed it. I would particularly recommend Guy Deutscher's book "The Unfolding of Language" (which is written for non-experts); he discusses how languages are in a constant flux being pulled in different directions by tendencies towards economy on the one hand, expressiveness on another hand, and there is a further hand or two.