A few reasons why you may wish to reconsider:
1. If you leave anything unattended that near Swansea, it will get nicked.
2. Codprawn, if he's still alive, will take loads of photos of you.
3. Mumbles pier is very popular with fishermen, who may land hooks, lead weights, beer bottles, etc. in your RIB.
4. IIRC private craft are not allowed to use the pier for landing.
If you're there at lowish water and the sea is calm, you could dry her out on the sand off Knab Rock slipway and walk ashore. There's lots of pubs, cafes, etc. at Mumbles where you could get your lunch, but don't leave anything of value on the RIB.