To a writer, ideas come often and the newest ones tend to sparkle a lot brighter than the ones we have been carrying around for longer. I have talked with and read advice from many writers/authors. While with writing it is necessary to focus especially when there are deadlines for projects, there are valid reasons for writing what you are enthusiastic about while you are experiencing the enthusiasm.
If you have lost that loving feeling for your current WIP, it might be time for a break. I am not saying to trash it. Sometimes a short recess is all that is needed to rekindle the spark that once had you working so diligently. When you lack the desire to write what is necessary, you are not going to be writing material that readers will be excited to read.
Do you have a process for rekindling that loving feeling when you and your WIP just aren't feeling each other?