There is a meaning of 「それまで」 that you appear to be unfamiliar with, judging from your paraphrase.
「それまで」, in this context, means "(that is) the end of the story" and for this meaning, it is very often paired with hypothetical forms such as 「～～と言われたら/言われれば」,「～～であれば/だったら」, 「～～なら」, etc.
My casual translation of 「好みの問題と言われればそれまでだが、私はこの店の内装はなんとなく好きになれない。」 would be something like:
"Even though it would be the end of the story if you said it was just a matter of taste, I just can't seem to like the interior design of this store."
The nuance is that the speaker knows that it is not him who has the final say on the matter but he wants to state his opinion anyway.
Your paraphrase 「好みの問題と言われても、私はこの店の内装はなんとなく好きになれない。」, however, means something quite different from the original. It means:
"Even if I were told that it was a matter of taste, I just couldn't like the interior design of this store."
This sounds as if the speaker still had some control over the matter. It sounds like he was complaining and sounds pretty assertive if not aggresive.