I really loathe wearing running shoes and I know ballet flats aren't going to get me anywhere... but I was thinking of putting in some gel insoles into my skateshoes to take to Europe..
Do you think that would be okay?
What about Converses (no laces)?
As long as they're comfortable for walking, they should be fine. My boyfriend wears skate shoes and I have both dark-colored sneakers (Skechers) and Converse. They aren't appropriate in some countries if you're going out for a nice dinner or some attractions, so plan according to your itinerary.
It's not sneakers that identify tourists, because many Europeans wear them.. it's how they are paired with other clothes. Search for "street style" and the cities you are going to, to get an idea of what the local fashion is like.