There is a lot to do at Alki. You can sail, play games, chill at the beach, walk in the forest and say hi to the wildlife, play in the park or on the water chute, ride the hot air balloon or the rope slide, get some music at the Coffeehouse… the list goes on. There are a ton of areas to sit and enjoy the scenery too, either with friends or by yourself. There is also a Japanese garden set aside, out in the water, where you can meditate or do Tai Chi, or explore the crystal caves below it.
The music events seem to run on a late (for me) SL schedule, 7pm SLT onwards, so I was not able to check out how popular they are. But there were still lots of people coming and going the whole time I was exploring here, so perhaps if you are the chatty type, it can be a good place to make new friends over a greedy board or dancing or whatever you want to do.