What verb represents acting with optimism, enthusiasm and vitality?
Try rally. The full text at the last link captures more of the optimism, enthusiasm and vitality you mention in your question.
2a : to arouse for action - M-W
1 (Of troops) come together again in order to continue fighting after a defeat or dispersion: 'De Montfort’s troops rallied and drove back the king’s infantry' - oxforddictionaries.com
When you hit that last mile in the race and are so tired you want to quit, that's when you rally, finding the strength to pick up the pace. - vocabulary.com