You have to consider, realistically, who benefits from someone's IDS talent. Mages (of which a typical raid setup will include 2); shadow priests (of which a typical raid setup will include 1); balance druids (of which a typical raid setup will include 1); holy priests (of which a typical raid setup will include 1, maybe 2); restoration druids (of which a typical raid setup will include 1).
A well-geared mage, in T5 or T6 level of gear, will probably have something like 320 spirit. 5 percent of that is only 16. Warlocks will have even less than half of that. Moreover, while you should be nice to your boomkins and shadow priests, you are not there to buff them. Holy priests and restoration druids would gain something like 25-30 bonus healing. You romanticize IDS if you think that is an important buff "later on."