Gold is a very valuable status, as it provides E+ at booking for you and a companion, free SDC, and Star Alliance Gold (lounge access internationally, and generally better treatment).
For the cheapest way to get miles, I would recommend the Mileage Run Deals forum. For the best way, I strongly recommend taking a short trip (couple of days) that you wouldn't have otherwise. Go fly to Hawaii for the weekend, or whatever piques your interest. It's much more fun than a flat-out MR!