The idea behind that spinnaker halyard rigging is that your mast is freely allowed to rotate even with the spinnaker up because your halyard pully slides around the side on the piece of Amsteel. On my 6.0, I have a tang (eyelet) from which my spin halyard pulley is mounted directly to like you are asking about. It certainly works but with the spinnaker up I have to induce positive rotation in the mast (you probably only have a rotation limiter). This setup you have, while requiring some maintenance, is superior. Those that I have seen like yours, however, have the piece of Amsteel drilled through into the luff track instead of internally in the mast making replacement much easier. There is usually enough room for a small knot behind the bolt rope of the sail.

The Inters and Tigers have a fixed sheave in the center of mast but have a bail several inches below the sheave that matches the curvature of the mast. (This is really hard to describe without a picture). The halyard runs under this 'bail' to the sheave and back down through the bail to the head of the spinnaker. The spinnaker can only hoist up to the bail because of a stopper ball but is allowed to rotate around the side of the mast. It accomplishes the same thing that you have but without the wear items.