I would like to buy some ninjago sets that are still available. Any ideas on what is a good set to invest in? Are any of the minifig sets that are still around worth getting like 9573?

Make sure to grab an Epic Dragon Battle before they go. I think the Golden Dragon is going to be awesome too. Those are brand new though, so probably no rush on that. These two sets would probably sell very well as a set once they are retired. As far as the Slithraa set in question, it may not hurt to grab a couple, but they are still available for a reason...

See my thread on the Golden Dragon set. That's my pick for a homerun out of the current run of Ninjago on offer based on the performance of the now discontinued Ice Dragon set. Epic Dragon Battle is another solid choice, especially if you can get it at a steep discount. Both these sets should see wide circulation throughout the year with frequent sales so pick your entry carefully. As always keep you eye out for any rogue discontinued sets to pop up that you can buy at retail and immediately flip for a quick profit.

Agreed that these two will likely be the winners of this set.

buy anything that can spin. buy anything that can fly