Ok, here is my take on it from two perspectives:
Experiential:
I used them religiously for many years and almost never missed a dose. I began to get lazy about it and stopped altogether after one water change. I never noticed a real difference afterward, even with pictures. I figured that just saved me time and money if I could get the same results. While at times polyp extension can be useful, it isn't always indicative of a good thing. I have seen some killer PE just before some RTN events, as well as after interceptor treatments. I don't know about you, but I wouldn't want to constantly run interceptor, either.
Chemical/biological: There is no evidence that corals actually need strontium, short of the fact that they incorporate it into their skeleton. Then again, they do the same with uranium, too. If anything, there may be evidence to the opposite--it may actually poison the corals' ability to optimally utilize calcium ions (I'd have to hunt the paper down). The same goes with iodine. The paper that all major companies use to quote the importance of iodine was based on dietary iodine, not soluble iodine. So basically it comes from what the animals get from food. There is also no evidence whatsoever that it benefits crustaceans. It isn't needed for molting, maturation, or anything relating to their exoskeletons. It will, however, cause them to molt more frequently, since it is a physiological response to get rid of excess iodine in the tissues. All the same applies to corals-- no evidence for use, beyond some incorporation. Chemically, iodide doesn't remain in that state when it reaches seawater--it actually speciates into three separate molecules (in ascending concentration)--free iodine I2; iodide ion I-; and iodate ion IO3-. There is currently no test to measure the levels of speciation that occur in aquaria--so you have no control over which form predominates, as well as their ratios. There is also significant evidence that food adds all the soluble and dietary iodine to an aquarium that the inhabitant would ever need (and then some).
The last part, however, I can most certainly agree upon every time--good parameters, light, water motion, and food are the real building blocks we have to work with.