2 pieces of advice here:
1) Take a look at the messaging from other companies (even outside of your market or industry). Who is really nailing it and what do you like about it? And who are the players that you still can't figure out what they do? See if you can start to incorporate some of the aspects you like into your message, or prune out some of what you didn't like. One thing I love doing here is seeing if there are ways to be more colloquial in your messaging. Especially if you work in B2B, see if you can incorporate some of the fun, down to earth messaging that B2C tends to do more of.
2) Don't be afraid to have your work torn apart. It can be hard getting feedback, especially for something you've spent a lot of time and energy on. But try not to get defensive or tune out what you don't agreement with. Go get feedback from the hardest critics. And don't be afraid to ask them follow up questions (ie "Do you agree with this point directionally or you don't think it's a main value at all?" "Do you have suggestions for alternative wordings?" etc)