Python is a programming language that lets you work more quickly and integrate your systems more effectively. You can learn to use Python and see almost immediate gains in productivity and lower maintenance costs.
If you discount the year or two it will take you to become as efficient in Python as you are now in the language you use. In a production environment, one seldom has the luxury of bot being productive for a few months.
You'll also have a harder time bringing new people on board because most people I interview to work with me are PHP programmers with no Python experience. It's been rare in my experience to have someone with Python web experience apply.