I agree Cryblood. I've never found any of the "R rated" trailers I've seen too be more effective than their 'all ages' counterparts.
And a good example of bad graphic trailer advertising are European cult film trailers. The Euro trailer for Fulci's ZOMBIE is 4-5 minutes long,and gives away the entire film(including the very ending/final shot) while also showing all the major gore scenes! If you've only seen this trailer and not the film,you already knew everything that happened in it!
Meanwhile the unrated but still less graphic/spoilerish U.S trailer which just has the title of the film spelling out,then goes into a brief montage of clips from the film and one brief head explosion glimpse before splattering the title and credits onscreen in one minute is far more effective!
Also Lions Gate releases alot of R rated trailers for films. I've seen one for High Tension which is terrible since it gives away too much and makes the film seem boring with how it's edited together. Meanwhile the all ages trailer while showing alot from the film shows it in quick montage and is incredibly effective and intense!
So be effective with trailers and don't show everything. You want to make people want to see the film. And that is by teasing them with the possiblities of what the film may contain.