Very interesting question! I think in these days, 正宗 mostly used to describe food, and more formal than 地道， like :正宗牛肉面，这家的烤鸭最正宗。 And 地道 can be used in more context，like this person is very 地道 （这人很地道,high compliment), means he‘s reliable and very honesty, It suggests I trust and like him very much. If you say:这人不地道，it means , he's really unreliable,and you highly doubt about his moral quality. You can also say 地道的英文简历，it means the CV is written in the way which the native speakers write. You can use 地道 with food for sure， we use it a lot ,much more than 正宗（正宗 is absolutely right), for example.:家乡的地道美食，这家味道真地道，这里的炸酱面很地道。 I feel people from Beijing used 地道 a lot.

正宗偏书面语，地道偏口语。差别不大。你的汉语一定很地道了。 ；）

其实应该没什么区别的，只不过地道更口语化，程度也比正宗稍微强一点吧。

谢谢！你们的答案都很有帮助。

地道 更偏向你达到了一定的标准， 我们可以说地地道道的中国人 （理解为是一个非常标准的中国人） 但是 正正宗宗 是不对的， 我们不这么说