I absolutely do expect multiplatform games to look better on PS4. Not by any drastic amounts, but noticeably. Even if you're a dev who doesn't have the time to learn how to take full advantage of the extra compute stuff the PS4 can do, that additional performance is still there. Taking advantage of it, if only for some more refined effects or what have you, won't take much work. And that's not even counting the discrepancy in memory bandwidth, which isn't exactly impossible to figure out what to do with. If you can move a lot more data to the GPU each frame, why wouldn't you do anything with that? It doesn't have to take months of extra work, it will basically just be like cranking up a few settings in the game engine.
Also, GPU compute is gonna start happening a lot more everywhere over the next few years. It's not gonna be some exotic way of doing things for very long, but rather the standard. The days of GPUs only doing graphics work are coming to an end, and Sony seems to be more prepared for that shift than MS.