If you only go to European capitals, it a lot of them might have a similar vibe, but from my experience you'll still feel a clear difference. Besides, there's the obvious change in architecture between the cities.
When you go outside the capitals, I'd say the differences can feel even more pronounced. Sure, if you do a long trip, you might have seen a lot of churches and castles, but I don't think it's any different to how you might get tired of looking at temples in Asia.
There's definitely lots of different places in Europe - if you go to Scandinavia, then visit parts of Central and Eastern Europe and then go Southwestern Europe afterwards, you can't help but feel a huge difference - especially as an American. However, due to the price levels being quite high in big parts of Europe and a similar Western cultural background, I'd probably - if I were American - go for more adventurous destinations before road tripping Europe