Thank you, Forero.
I was taught of such a sentence(the following one), could there be something similar to my topic sentence? Further, is the following one correct? I think it here is a dummy object, am I right?
We call it a dummy subject when it is used in place of the subject to allow a (long) subject to be delayed.
I think we discussed the it in "I hate it when he sings" in another thread. It is not a place holder to delay anything. The meaning could be that I hate the noise he makes when he sings, the trouble his singing causes, or the fact that he is singing. To me, this it allows "when he sings" to mean "at the time(s) he sings" by blocking it from being the direct object of hate.
Some native speakers give no meaning at all to it in such a sentence, but without the it, I take "I hate when he sings" to mean that I hate the time(s) at which he sings because the when clause has to be the direct object of hate.
In the original sample sentence, "that they are valuable" is unlikely to be adverbial and must be the object of on, which leaves no purpose for it.