After years of design work, many of my presentations start to develop a similar signature style or look-and-feel. (Secret: it looks remarkably close to the templates in SlideMagic). I think there is nothing wrong with that: you can easily recognise the work of famous poster designers, painters, architects. Presentation designers should be no exception.
I would encourage you to find your own signature style. Once you have figured out a distinctive way to make any chart look good, you are free to focus on its content. No need to worry about fonts, image crops, data chart layouts, and all the time to worry about composition, content, what image to put and what data to visualise.
Art: detail of Gustav Klimt, The Kiss, 1908