I think you should ask yourself:
* Which game(s) have performance problems? On which devices?
* What do the profiling data tell you about the location of the problem(s)? Hopefully you can get a native profiler on all your target devices.
* What is the best way of fixing the specific problems?
If the answer to all of those points to a STL custom allocator being the BEST way of fixing the problem, then do it. Otherwise don't.