You should always appeal. Cite the (temporarily) low interest rates that lead to your inflated purchase price, and document all of the comparable properties in your neighborhood that are assessed at less. You should expect to waste a day or two (8-16h) fighting it, but presumably a perpetual 70% increase to your tax bill is worth that. Get a court date if it comes down to it. You will probably be able to settle for a light fucking instead of the whole thing.

If no one fights, the city uses the assessment of house A to increase the assessment of house B one year, and then use the increased assessment of house B to increase the assessment of house A the next. The city wins eventually either way, it's only a matter of how quickly and arbitrarily we allow them to rip us off.