"Can we be spiritual but not religious?" Jesus and Mo say no, I say yes... and I have strong ("bright") allies in Richard Dawkins and Dan Dennett.
If by "spiritual" you mean something like, "outside of space and time, and continuous with the same conscious memories and experiences forever," they agree: No, we can't.
But, if by "spiritual" you mean something more like "alive to our actual place in an evolving cosmos, unblinking in the face of personal mortality but fully open to the possibility of some naturalized sort of transcendence or other," they agree emphatically: Yes, we can.
(But be forewarned: the video techs intrude themselves regrettably into this uncut post, and really disrupt the flow of a very engaging conversation, about ten minutes before the end; but stick with it, or "ff" thru it... the end is well worth suffering the annoyance. Dawkins' reading from his Unweaving the Rainbow definitely belongs in an anthology of humanist "hymns" that will certainly include Carl Sagan, John Dewey, Bertrand Russell, and all my other favorite philosophers. But, somebody please slap those techs for me!)
Oh, by the way: Dan Dennett, like Jackie Robinson and William James and many others on whose shoulders we humanists proudly stand, is another pragmatic meliorist in the rich American tradition: there's plenty of goodness is the world, but it needs more. Let's make some.