I've walked the entire Frances once, and I've walked the part of the Norte from Pasaia to San Sebastian/Donostia maybe a dozen times (part of the first day, one of the most difficult days of the Norte). While most routes have a fair bit of pavement, they also have a large amount of dirt, especially when climbing. The route between Pasaia and Donostia would be particularly difficult to do without hiking boots in my opinion. My son fell over and over and over in tennis shoes. The next time we bought him some hiking boots and he didn't fall once. Because of his age (he's only four years old) he isn't the BEST example, but using my own judgement, I, personally, have resolved to ONLY do the Donostia-Pasia section in hiking boots.....and that is only a 12 km stretch. I'm sure there are plenty of other stretches where hiking boots would be far preferable to tennis shoes.