As someone working for the Science Museum, who
Kew want to change their mission statement from:
"To enable better management of the Earth’s environment by increasing knowledge and understanding of the plant and fungal kingdoms - the basis of life on Earth."
... to the slightly more succinct, and subtly different ...
"To inspire and deliver plant conservation worldwide – enhancing and sustaining the quality of life"
The key differences, to my eyes, are a re-focus on 'inspiring' rather than 'understanding', which is more of a public role than an internal academic role. Inspiring is something that museums, and places like Kew Gardens (which I guess is a living museum) can do well. Inspiring is a term that you associate primarily with the arts, where musicians and painters can inspire each other, but also has a general sense of prompting people to do positive things. In the museum sector, the kinds of things you want to inspire people to do include seeking further learning (formal or informal), creative activities (making art) and innovating in some scientific/technological/business sense.
Kew want to inspire 'plant conservation', which is quite specific, but the aim - to enhance and sustain the quality of life - is quite wide.
The degree to which mission statement really mean anything could easily be debated, but if you are going to have one, then the idea of seeking feedback from staff and supporters is surely a good idea. So if you have strong feelings (maybe 'fungi' should be specifically mentioned after all), then let them know.