Yes, I think the Island wanted to test Locke..to take away what it had given him in order to reaffirm his faith in the island. The island seems able to discriminate - it heals who it wants and makes sick who it chooses. As you mentioned, this is particularly signified with the healing of Locke's paralysis and the tumor in Ben's spine. Ben eventually admits to John that "the island wanted me to get sick and you to get better" (or words to that effect).
With this in mind, it would seem that the island bases it's decisions around a best
course of action approach. It is chasing in a long-term goal, which may ultimately be presevation (survival), and to do this it needs a chain of events. Locke being a 'chosen one', it is imperitive that his faith in the island is strong. As we saw in the finale, Locke still needs ALOT of guiding (as Ben did EVERYTHING, bless him), so the island shapes and coerces him accordingly..as it does with others.
A
sacrifice or two may be needed along the way, but it's for the greater good, in that no event is singular..every event has a consequence, hence an entire chain is needed to facilitate the end-game.
In my view, that is.