No, Seaside's design has always been a little electic with a touch of modern. and the square and large buildings do bring Sienna or other larger Italian piazzas to mind, but in a beachy way.
You said it just right. Seaside is a great blend of styles and even though it has become an adjective (i.e. "Seaside- style" this that or the other) it really has emcompassed lots of influences, not just the old southern beach house, exclusively. I think the "feel" they are attempting to cultivate might be described as "Italian" in that they want the plaza to teem with life.
Ruskin Place has been around for a while, and I never hear anyone talking about how cottagey it feels, nor how modern it feels. I like it very much and it looks just as much a part of Seaside as the cottages. It seems natural to have higher density buildings near the town center, with single family residences on the outer edges of the community. If Seaside were larger, perhaps we would also see much larger estates on the outer edges, just like every old city in Europe. I guess we are too used to seeing an entire development completed in less than two years, so seeing more completion of the original development of Seaside, over many years, feels more like it is changing, rather than like it was part of the grande scheme.