the saves do help and flesh out the story quite a bit in some cases. For example helping a faction or someone surviving at the end of ME2 will influence and help you in the final battle in ME3. IE: Getting the 10000 you need to get the best ending. I can certainly see getting the ME2 DLC and completing it in a satisfactory level will benefit you.
Plus its your personal adventure and it will make it a more personal experience. Some more then others, but its still a nice touch and adds depth to the game.