It's hard to tell where the following breaks up as it's in one bubble.
Anyway. My attempt at (somewhat literal) translation here is:
Because it's troubling, how about if we went to the store?
It is necessary, 山田 having existed.
The last part makes no sense.
I'm not sure what the connective だって or the せっかく are doing here. Or the last だろ, for that matter.
A new translation based off information provided in the comments:
Because it would be a shame not to, how about about if we went to the store? I guess 山田 needs to as well.
The character is responding to one a question from another character who is wondering if everyone has a certain item.
P.S. I've avoided mentioning the source because of the absolutely humiliating nature of the translation assignment (the same one as my classmate's from other posts, it turns out). I'll give a link to on one image, but caution you against reading the series. Unless you have morbid tastes.