Spinning can do anything. Spinning gear catches marlin and tuna. It depends what you want, what you like, and what you expect. 1) Heavy-duty spinning gear is usually physically heavier than the same casting gear. The recently-introduced long fiber carbon spinning reels may change this, though. 2) With weightless presentations, spinning gear lets the bait sink vertically. Big advantage in my book. 3) Spinning gear is used by your strong side. This is a big advantage in high-torque presentations, like twitching, snapping and jerking. 4) Casting gear puts its weight closer to the fulcrum point of your hold, so it causes less fatigue with a high-resistance retrieve. Spinning gear can partially overcome this simply by aiming the rod at the lure and retrieving straight-line. You sacrifice the rod's shock absorption abilities, though. 5) Into the wind. This is the big one for me. Spinnerbaits, crankbaits, soft plastic .... it makes no difference. You never have to worry about a backlash with spinning gear. You may have to worry about wind knots, but that's another matter. 6) It's easier to design drag capacity into a spinner than a caster. For higher priced reels, there's not any appreciable difference. But on the cheap end, spinner drag is usually smoother. I don't know about you, but I appreciate a smooth drag that's low poundage much more than a strong drag that's erratic. 7) The one huge advantage casting gear has over spinning gear is handling large diameter mono/copolymer line. There are people on this site who religiously use braided line. They more or less have the opinion that mono is outmoded. For better or for worse, I'm not one of those people. I love monofilament line for situations that need "give". I also hate the abrasion characteristics of braid. So for heavier line, I use baitcasters only, and they're spooled with mono. You can use spinning gear for large-diameter mono, but see #1, above.
Lots of people will tell you to give it a try, and they're right. Try it. But your original question was, "Am I missing out by just using these?" If you're talking about limiting yourself to 1/2 oz. lures, then YES. If you're talking about using spinning gear, then NO. jj