I see that you haven't specified which frequent flier program this is in.

I also vote for trying for a reroute on your existing itinerary.

That said, take a look at the Mileage Run forum for past topics' guidance. In this case, spending a hundred dollars on a cheap ticket anywhere to get you over the 50,000 mile threshold this year could pay off not only in the sometimes difficult to quantify benefits that "Gold" status confers for next year, but also in the additional bonus miles on all your planned travel next year. If you expect to exceed 50,000 actual flown miles next year, that can be a big chunk of bonus miles to give up.