In strict usage this should be either
If we go somewhere else it will be different ... or
If we went somewhere else it would be different.
But informal use is not so demanding. In conversation, sentences have to be constructed "on the fly", without looking so far ahead that strict correspondence can be maintained. The writers/actors here reproduce this very accurately:
BANYA: You know, Jerry, I was thinking for our next meal, do you think we should come here or should we go someplace else? It has its pros and cons. On the one hand, here, you're guaranteed a great meal. On the other hand --
JERRY: Yeah, yeah, I know. This would be good, but it'd be the same. If we go someplace else, it would be different, but maybe not as good. It's a gamble.
The conversation is about choices and contingencies, where it is perfectly normal (and perfectly grammatical) to employ past-form modals with non-past reference. The parties understand what is being said without requiring strict consistency of tenses. Strict form is mandatory only in writing, where the author cannot intervene to correct the reader's misunderstandings and must therefore employ every available convention to insure that no misunderstanding arises.