Is it worth mitigating against the effects of garbage collection?

This is similar to the flyweight pattern detailed in the GoF patterns book (see edit below). Object pools have gone out of favour in a "normal" virtual machine due to the advances made in reducing the object creation, synchronization and GC overhead. However, these have certainly been around for a long time and it's certainly fine to try them to see if they help!

Certainly Object Pools are still in use for objects which have a very expensive creation overhead when compared with the pooling overheads mentioned above (database connections being one obvious example).

Only a test will tell you whether the pooling approach works for you on your target platforms!

EDIT - I took the OP "re-used wherever possible" to mean that the objects were immutable. Of course this might not be the case and the flyweight pattern is really about immutable objects being shared (Enums being one example of a flyweight). A mutable (read: unshareable) object is not a candidate for the flyweight pattern but is (of course) for an object pool.

Normally, I'd say this was a job for tuning the GC parameters of the VM, the reduce the spiky-ness, but for mobile apps that isn't really an option. So if the JVms you are using cannot have their GC behavioure modified, then old-fashioned object pooling may be the best solution.

The Apache Commons Pool library is good for that, although if this is a mobile app, then you may not want the library dependency overhead.