to me the simplest is to pick a hieght impaired crew! - Boom Boom! {Sorry about that!}
Not knowing 'Blithe Spirit' beyond what I believe is gained from a bottle - this is only hear say, as I tend to preffer being a tea wozer!
Anyhow now I got that out of my systern.
Using pullies, counterweights, fishing line & other  simple  bitts & bobs on hand, can work wonders & gaps of "How did they do that?" is what's it's about!
Can you give any more specific info of what you would envisage happening? {for a thick as a brick &completely  spiritless wombat - like me!}

We used  keyhole shaped holes in two different flats behind paintings which were hung by an handle thru them.  When the paintings were just hanging, the handle was fitted in the keyhole.  When it came time for the pictures to move on on the wall, someone behind the flat lifted the picture up by the handle and wiggled it around.  We also popped books out of the bookcase by running fishing wire behind the books we wanted to pop out, and then when we pulled it taut, it pushed the book out.  (Required some finessing of stationary books:  we made glued,false fronts for the stationary book and drilled them to run the line thru the front edge.  Then the line ran behind the moveable book, and then thru the false fronts onthe other side ...and then thru the flat so someone backstage could pull it at the right time.  We had a peg holding up the curtain rod over the french doors that we pulled so it would fall (pulled from behind a flat again.)  There was a foot pedal under the table that lifted and knocked from underneath (I think it was similar to a drummers foot pedal)  I don't remember how we rigged the door to open, it was a counter pully of some sort, but as I didn't understand it then, I cant explain it now.  Most of our effects were from directly behind the affected flat by the stage crew (or an actor, as the ghosts aren't on stage in the final scene)  I hope this wasn't too muddled.  I'm not terribly good at explaining things. 

For us, we used french doors and attached small cables and pulleys in a loop pattern for them to open independently. the bell on the fireplace mantle was set on a mouse trap with a removable pin, launches very well. There were pictures on a shelf that had monofilament attached to the shelf, then under the frame from the front, over the top, back down to a hole through the wall under the shelf. The one I liked the best was with the pictures. We had one rigged with a small bungee cord at the bottom, pull pin also at bottom, and launched it in the air.

Don't get me wrong.  I think the silk and suture are very good ideas, and I look forward to trying them.  But I do have to disagree about the fishing line.  Old school fishing line was shiny and came in about three tints, blue green and off-clear. I agree: too shiny.  They now have line designed to not reflect light (apparently fish are getting more savvy) and they have super strong weaves like spider wire (comes in dark colors).  Much can be accomplished with these, especially if the set designer really helps to disguise any  possible sight with textures and colors.  I have seen really crappy effects that show the hows and whys (curled fishing line hanging from the ceiling), and I have seen some really spectacular effects that made the audience crowd around the stage and block the exits after the show, because they were trying to see how it was done.