I got waivered to SPC in January this year. What correspondence courses and other training will help me benefit my unit

Do what you are currently doing to stand out. Correspondence courses usually don't coincide with unit success. Just be a leader

College > Correspondence IMO. Those promotions points are not going to help you with anything once you get out.

Correspondences will only help you in your career to help you get promotion points for SGT and SSG. Check skillport and do what you want to learn to better yourself. If there isn't anything specific then just do as many as you can to get the maximum amount of points for promotions points.