I would absolutely recommend against excessive positivity and optimism. Any positive emotion that you're infusing into a workplace needs to be grounded in reality. If it's not realistic, sincere, meaningful, and individualized, it won't do much good.
Wanting a more positive environment isn't enough. You need to do something, and it doesn't require a great deal of effort or some huge change in the way you approach things at work.
Positive defaults align our short-term decisions with our long-term interests. And we don't always do that.
Positive defaults protect you from yourself - and that helps you to make decisions in the moment that are better for your long-term interests.
Simply try to turn your next conversation with someone who is negative into a more positive moment. See what happens. In most cases, they will turn around and be more positive in their next interaction.
If you want people to understand that you value their contributions and that they are important, the recognition and praise you provide must have meaning that is specific to each individual.
Positive words are the glue that holds relationships together.