This form implies a 'Que" as in: "Que le vaya bien".
[Que] valga esta jaculatoria como x etc. [the comma is wrong, in my opinion]
- Let this be a short prayer as x
- May this then be a short prayer as x
This subjunctive form has three standard translations into English:
- May x [be something or happen]
- Let x [be something or happen]
- Let's hope as in Ojalá le vaya bien. Let's hope everything turns out well. May everything turn out well.
The sentence with valer jaculatoria is difficult because of the valer.
Que valga la pena decir todo esto.
Let's hope saying all this is worth it.
Que valga dinero lo que estás haciendo
Let's hope what your doing is worth money.
[Que] valga esta jaculatoria como
Let this short prayer be [have the value of] x
I hope this gives you a better feel for the text.