Think of it like this:
G-d runs the world, and he does what is best for us. And he loves us, and is kind, and generous. G-d sometimes puts us in hard situations, because that is what is best for us, and sometimes that is in order that we should daven to him and become closer to him because that is what is best for us.
Now, does it make sense to you that even thought that is true, if you do some trick, like paying someone to daven for 40 consecutive days, or davening yourself for 40 consecutive days, or doing challa with 40 other people, that you will circumvent G-d's plan?
Or does it make sense that what G-d really wants is for you to daven 40 consecutive days in a certain way? And if they aren't consecutive? And if they weren't all in amuka?
Or to say shir hashirim for 40 days?
In legal terms, we would call that sort of action "arbitrary and capricious". Do you think G-d is arbitrary or capricious? Don't you think G-d wants us to be normal and do our best and just keep the mitzvos like chazal said to and daven like chazal said to? Is he so arbitrary that if you happen to do some trick, then you can circumvent what is really best for you?
Look, daven at the kosel, say shir hashirim, say tehillim, make challah--but do all these things because they are a mitzva. Do them because Hashem said to. Do them because they improve your middos and perfect you so that you can be like G-d, imitatio dei, mah hu af attah.
Or, as Hashem told us: תמים תהיה עם ה
(P.S. You should all read the book by that title written by Rav Yaakov Hillel where he excoriates mukubalim.)