Look into some of the pruning development discussions that are happening, if you haven't already [0]. I believe it's a question of when, not if. Probably, only a few nodes will end up needing to keep the full merkle tree, that others can then use to bootstrap. But then, a few full, original nodes are all your service really needs, too.

0. http://thread.gmane.org/gmane.comp.bitcoin.devel/2065