|If your manager truly believes that your work is insignificant, then he is actually making a negative statement about himself as a manager. After all, you presumably receive your assignments from him, and if he emphasizes how insignificant they are, one can only wonder about his ability to identify and assign meaningful work.|
Since you truly believe that your work is significant and makes viable contributions to the company, one key step is for you to document these accomplishments for your manager, since he appears to be either uninterested or incapable of seeing them on his own. As for future projects, you should identify and describe the potential benefits and value that will be generated as a result of your successful completion of this work.
After you complete a project, you should continue to track the benefits that accrue from it. When you provide such information, it should not be in the form of a boast, but rather as a factual update that lays out the clear, specific, and measurable benefits that are being generated. Your manager does not see the glass as being half-empty or half-full. Rather, he hardly sees the glass at all, and hence you need to pour out the information for him.