$750.per year more. Well, how long are you going to stay might matter.
But really, it the value goes up you win, but then you need to pay higher taxes.
1) yes, if you chose to fight you can dispute the space. However, you might not win.
2) yes, the new sq.ft. should show in the public record.
3) when you sell you will use the new sq.ft.
You might as well work on fixing the issue and not fighting it. Adding the sq.ft. will add to your bottom line in the future.