You explained my ideas :))
I discuss it with my boss sometimes, I say 'they will share code' and he say 'they will use black boxes'.
My arguments are start-quickness of new coders, code sharing, work effectivity (ideally, no wheel reinvention), less amount of code.
His arguments are laziness, black boxes, impossibility of usefull interface design and the potentiality that nobody will be able to hack old, heavily shared libraries/modules.
But I think that good documentation and voluntary on-the-job training can boost my arguments.