Full length battens have an advantage on really fast boats where the speed of the boat really affects the apparent wind. For most keel boats smaller than 45 feet or so, I think that there are significant advantages to a 2+2 set-up.
On my 30'' ULDB (1995 vintage), I switched to a full upper batten last summer to fix a "hinging" problem with the long top batten. This helped to get another season out of the sail, but caused problems with the backstay...another step to take while tacking. I definitely would not want full battens on the lower three. However, lately, I have been sailing on a 43'' offshore racing trimaran, where all battens are full, and on this boat full battens are a real necessity. By design, there is no backstay to deal with as the boom extends aft of the stern. There are some very hefty running backstays though.