Connective だって and use of せっかく


It's hard to tell where the following breaks up as it's in one bubble.

> まあまあ  
>  せっかくだから[買]{か}いに[行]{い}ったらどうだ  
>  [山田]{やまだ}だって[必要]{ひつよう}だろ

Anyway. My attempt at (somewhat literal) translation here is:

> Now now,  
>  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.

**EDIT**

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.

<http://mangamatome.tv/view_9995_3.html>




My translation would be:

> Well now,
>
> since we've come all this way, how about going to buy one (bathing suit)?
>
> Anyway, Yamada needs one, right?

Without reading the entire comic in your link, I am guessing that getting to
the beach was kind of a journey. In this case `せっかくだから` means something like
"since we've already done this difficult thing" or "since we traveled all the
way here", etc. `だって` with someone's name can serve to call attention to that
person, pointing them out amongst others to remark about something concerning
them that may be unique or special -- in this case, the fact that he has no
bathing suit and that the previous statement directly applies to him.




My translation would be:

> Well now,
>
> since we've come all this way, how about going to buy one (bathing suit)?
>
> Anyway, Yamada needs one, right?

Without reading the entire comic in your link, I am guessing that getting to
the beach was kind of a journey. In this case `せっかくだから` means something like
"since we've already done this difficult thing" or "since we traveled all the
way here", etc. `だって` with someone's name can serve to call attention to that
person, pointing them out amongst others to remark about something concerning
them that may be unique or special -- in this case, the fact that he has no
bathing suit and that the previous statement directly applies to him.

