I just had my rear shock rebuilt and resprung at GMD Computrac. (No affiliation , no reward for new customers, no remuneration, etc.). I went with a heavier spring because I am heavier than the average bear. Kent, the gentleman I worked with, explained to me that with a heavier spring I would need to go with new valving because 1) the old valving would be worn and 2) the heavier spring would be too much for the stock valving. I went up 18% on the spring rate and it made a huge difference. I am going from memory here, but I believe Kent told me the stock spring was in the neighborhood of 950 lbs. He also told me that the springs on our shocks loose very little "spring" over the years. It is the breakdown of the oil and valves (which are nothing more than extremely thing washers acting like reed valves in a 2 stroke engine) that causes us to become unhappy with our shock's performance.
Kent did the respring, revalve, and rebuild of my shock for $453.00. Total cost. I am very happy with the results and will use him again and again. If you are interested, he is in Jasper, GA.
BTW, I don't in any way mean to obfuscate the results of those who resprung without rebuilding. I haven't tried respringing alone, and it may have worked out just as good. Our front shocks are not serviceable, so who knows, I may try it just to see. It certainly is cheaper than a new shock and well worth a try.