But it would take much more effort to catch those asteroids, if I am not mistaken? They do travel a wee bit faster and on more eccentric trajectories than the asteroid belts ones, plus they are a lot smaller and contain lesser proportions of useful stuff?
No, it's actually substantially easier to reach NEAs than main belt asteroids. There are NEAs that are much more difficult to reach, but the easiest NEAs to reach require round-trip delta-Vs less than those required to reach the Moon. These comparatively easy targets have a less eccentric orbit, an orbit that to begin with is rather closer to the Earth's, and a less inclined orbit than most main belt asteroids. Also, it's not absolute orbital speed that matters, but relative orbital speed, and the NEAs have an orbital speed much closer to Earth's than any main belt asteroid. Think about the relative delta-Vs needed to ballistically reach Pluto versus Mars, for example; the former requires much more of a kick than the latter, despite having a much smaller actual orbital speed, because the relative difference with Earth's orbital velocity is much larger (so the change in energy needed is much larger). So if you want to reach 1943 Anteros, 433 Eros, 1950 DA, etc. (NEAs), then that's easier to do than 1 Ceres, for instance, even if 2000 BD19 (also an NEA; actually, the NEA with the distinction of approaching closest to the Sun) is a lot harder. The best NEAs are easier to reach than the best main-belts, though.
Size is actually not particularly a disadvantage. It's not so much that the NEAs are smaller per se, it's that the biggest main-belt asteroids, like 4 Vesta and 1 Ceres, are larger than the largest NEAs. But 433 Eros, for instance, is 34 kilometers long and 11x11 kilometers in both other dimensions, which is quite large in an absolute sense. For that matter, even a 1x1x1 kilometer asteroid is pretty big, and there are a lot of those among the NEAs (well, asteroids pretty close to those dimensions). A particularly small asteroid may be reasonably practical to move into an Earth orbit to allow easier access, as well, something you're just not going to do with, say, Ceres, at least not in your lifetime.
Resource-wise, the bag is more mixed. We don't have a complete census of NEAs, particularly at the small end. There appear to not be many highly metallic NEAs (1950 DA is one of the only ones), but there are a few. I'm not sure about certain other types which are interesting vis-à-vis resources (like carbonaceous chondrites or other volatile-rich types). The most interesting resources for now are platinum-group metals (which tended to end up in Earth's core at the formation of Earth) and volatiles (because you need a lot of them in space). If iron and steel were ever commercially extracted and manufactured in space, it would mostly be for space-based projects and after quite a lot of development in space to enable the relative marginal cost of doing so to be very little (or an attempt to recover value from the "slag" left over after extracting PGMs from a metallic asteroid, which would mostly be iron and nickel).
