How do you check how much power one of the nodes has? I remember reading somewhere that you shouldn't drain an astral node past a certain point because then it takes a long time to recharge fully...

And, that aside, at level 69 should I even be up on Astral bashing lobstrosities (because that's all I can fight confidently)?

The room description tells you. Crackling with power and rainbow halo are both fine to link. Anything else you really shouldn't.

And if you can bash them, then why not do it?

Course, that raises the question... how long should you link them before you should stop so that you don't overdrain?

Crackling, rainbow = feel free to link because the node will regenerate power quickly.
Motes = You can link, but watch that you don't drain it below this level.
Anything else = don't link because it'll take forever for the node to regenerate its reserves.

You shouldn't really even link motes.

What he said.

Linking motes is only cool when you need one or two more critters for the next level.