Bluesound Node2 with outboard DAC

Should I do that or get a node 3 and upgrade the power supply in that?  Is it even worth it?

IMHO, no.  Rather than polish the turd use the $ and save up for a better streamer that’ll already have a better power supply and other components that’ll improve performance.  

Agree with keeping things separate.  Pairing the Node with a DAC from Gustard, Musician, Denafrips, Soekris, etc. (depending on what sonic characteristics you’re after) will give you a nice performance bump and then upgrade streamer when you can.  Also, don’t discount the importance of the digital interconnect between the Node and DAC as it can have a big impact on what you ultimately hear so don’t skimp there.  Best of luck.