It really is a personal decision, and varies based on your own circumstances. Are the limbs in very good or better condition? Maybe you could sell them and buy another set in a weight you prefer for the same money it would take to have them reduced. If they are in need of a refinish anyway, weight reduction starts to make sense.
Are the limbs and/or bow special to you in some way? Was it a gift or have special memories connected to it? Sometimes bows are just tools, other times we become pretty attached to our possesions for many different reasons.
Also, ask yourself if you are sure your shoulder problems are permanent. Often times therapy and/or surgery repair old joints. Is there a chance you might be able to use the heavier limbs again someday? If so, that tips the scales in the direction of a new set of lighter limbs.
John Rafferty (jcrafferty) is the new owner of the Bow Hospital (formerly part of Prairie Traditions) and could sure help with a weight reduction if you do decide to go that way.