I'd disagree with that - from their point of view, the plan is to eliminate all religions except their particular radical brand of Islam. So it wouldn't be pointless at all.
Of course what they'd really like is a knockout blow to the West (or a series of them if necessary), since the West is the biggest single thing in the way of that plan.
True, but in Indonesia a large percentage of business is dominated by ethnic Chinese Christians. Last time they were attacked (1998), the Chinese split for Singapore with their money and never came back.
In the ensuing economic meltdown, a lot of Indonesians were financially hurt, and the bombers learned their lesson ... sort of. The economy has never really picked up since then.
More bad PR for the Islamists, but they have short memories.