So I do an STB extraction. I like it a lot and I try to reuse my naptha several times. However, it gets to a point where the naptha is starting to get a little darker and I retire it, put it in a pan, put a fan on it and wind up with brown oily residue that smells like a spice mine, the naptha is definitely gone.

Now I'm not a chemist, but I play one in my garage and I'm pretty sure that gooey puddle is DMT and plant oils, my question is... is there an easy way to separate the oils from the DMT now or should I just re-dissolve the goo with acetone, chuck in some mullein and flowers, let the acetone evaporate and call it changa?

You could do either.
If you want to isolate the NN, try washing the residue with room temperature heptane. Evap the heptane and you should be left with fairly pure DMT. Or you could go for a full blown recrystalization

It looks like I could score some Bestine solvent... when you say "wash"... what exactly does that entail? Just re-dissolve & decant? The heptane won't dissolve the oils then? Or it dissolves the oils and evaps them too?

Thanks for all your help.

It's kind of a short cut recrystalization.
You just pour a little bit of heptane on the dish with your goo and mash it around. The heptane is far more selective for the DMT than for all of the other gunk (some of which is quite active) that the naptha picked up. The undissolved bit will start to firm up as the heptane dissolves the DMT. Once it seems to stop getting firmer, pour off the heptane and let it dry. You should be left with some more crystals and the remaining residue should be a lot firmer and easier to work with.