In the second bracha before Shma in the morning, there is a line which is taken from Tehillim 86:11 which reads, "יַחֵד לְבָבִי לְיִרְאָה שְׁמֶךָ". The construction I found in the Artscroll reads (I am copying it from the Online Siddur which has the same text) "וְיַחֵד לְבָבֵנוּ לְאַהֲבָה וּלְיִרְאָה אֶת שְׁמֶךָ". While I see why the prayer text would add an introductory vav (assuming that the phrase in Tehillim starts a new sentence but in davening it is a continuation) and why the prayer version would be in the plural), why would the word "et" be inserted in the davening version? My siddur (Siddur Tefilla Hashalem) in fact omits the word and keeps the phrase as in the original, "וּלְיִרְאָה שְׁמֶךָ" (though it adds the vav).
What is the difference in meaning that would drive one siddur to insert a word into a pasuk but not another? Is this "et" significant?
I don't think that this is an isolated moment attributable to the vagaries of editors, but that this was a reasoned decision. If I understood the decision, that might lead me to see the subtleties of meaning created in this specific case, and if I understood the specific differences created by this case, i might see what drives an editor -- so an answer to either the general or the specific question would be appreciated as it would provide insight into the other question.