>I read about SP accumulating something just sitting there but I still don't know if and how this works. After a certain threshold perhaps.

About 16% of the reward pool is paid in interest to Powered up Steem, there is no threshold. If you do nothing, you will see your wallet tick upward.  

>Anyway, it's the power to curate, i.e. support people and that on itself is great, so that's why I prefer turning almost everything into SP and I wait for the times when my support is going to matter. Will be awesome :)

I remember when mine was making a lot more difference, it felt great. However, the interesting thing is that at a Steem level, I am distributing more now. :)