I think it would be nice to spice up wormholes. Here are some ideas I had:
1. Wormholes seem to last forever. Esp. after the event that creates lots of them, the map (or at least a certain part) is often littere with them. What about making some disappear after X turns (= these are not stable).
2. Wormhole rides are not for the faint-hearted - on a rare occasion you lose the ship going through a wormhole
3. OTOH there could be very rare, but stable wormholes. Ideally these would get a colored symbol after discovery (so they should not be known as stable from the start, only after someone did use it 1st time).
These would not go away after the 1st wormhole ride, but provide a permanent connection between two points (not sure if the AI can hadle this though). If "permanent" feels overdone there could still be an event that makes those collapse, giving the player a info msg. though