Hiya Henry, i used to work at the ace cafe, its a great place to hang out and meet new bikers.
The member ship is not worth it if your not a regular, you will only get 5% off a meal (which isnt much) seeing as there prices are a bit high. The food is ok, when its cooked properly it can be quite nice lol.
If your looking to go there at a quiet time then any day during the day time is good, if you want to go at a busy time then as everyone else has said, friday nights is the night.
you dont need to worry about the safety of your bike, you can park it at the front where you can see it. The stunting has been banned from inside the car park so theres no fear of another bike crashing into yours.
Hope this helps