If you do choose to fly without the spinner installed, make doubly certain you aren't bottoming out your prop bolts before reaching torque values on them. Some prop bolts (especially wood/composite fixed pitch) depend on the thickness of both front and rear spinner bulkheads plus the crush plate to take up the grip length of the bolts. Really, really bad things will happen if the prop bolts bottom out and the prop is not properly secured to the crankshaft.
Several years ago, a friend of mine in an RV-6 had a suspected bird strike that took most of the spinner cone off in flight. I was flying behind him in my old Cherokee when it happened. All he knew at the moment was there was a loud bang followed by excessive prop vibrations. He slowed down so I could pull alongside and I noticed his spinner was gone! Fortunately there was an airport just a few miles away so he throttled back to reduce the vibrations and landed normally. There was a small piece of fiberglass still held on by a couple screws but it was enough to throw the balance off quite noticeably. We removed the fragment of fiberglass and the remainder of the spinner screws to get the balance back to something useable, and he flew it home. He said with the spinner cone now totally off he could run normal RPMs without vibration, but did notice some added drag and reduced airspeed. No noticeable increase on the CHTs either, but he only had a 150hp O-320 which was not known to be a big heat producer and it was a fairly cool day.
So... you might get away with limited amount of flying an RV without a spinner under certain conditions, but it's highly inadvisable to do it on purpose as a matter of routine operations.