I don't think any sole manga/anime has really affected my way of thinking or anything, but some of them really open you up to new things. I watched Sakamichi no Apollon on a whim and I loved it. If it wasn't for that I probably wouldn't have any sort of taste for older music, jazz or just different genres of anime in general.
If it's any colsolation I recently started watching Uchuu Kyodai which is really inspiring, even if I've only seen two episodes of it so far. Stuff like it's never too late to give up on your dreams and you're not going to get anywhere if you don't at least try, it's beautiful, really.