What is the dramatic importance of Rosencrantz and Guildenstern,the Players,and the Grave-diggers in William Shakespeare's Hamlet?

There is much in the plot of Hamlet
that highlights proper behaviour for one's station in life, especially if you are of the
royal family.  Gertrude and Claudius chastise Hamlet for his very un-correct display of
grief in the very public Act I, scene ii and Polonius not only lectures Laertes about
proper behaviour, but has him spied on to ensure that he is behaving as a man of his
position should.

So, one of the importances of R&G
is to demonstrate the "proper" way Hamlet should be behaving.  We
can assume that they are very close in age and station to Hamlet, and they do whatever
the king says, even strong-arming Hamlet out of Denmark as a part of a plot to end his
life. All in allegiance to their king.  Acting out of blind allegiance is the last thing
Hamlet would do.

As for the players, part of their purpose
is to highlight Hamlet's inability to act on his feelings.  When he comments that one
player is able to create (from his imagination) all the proper behaviour for
nothing,

For
Hecuba!

What's Hecuba to him or he to
her

That he should weep for her?  What would he
do

Had he the motive and the cue for
passion

That I have?...

Yet
I,

A dull and muddy-mettled rascal,
peak

Like John-a-dreams, unpregnant of my
cause

And can say
nothing.

he calls attention
to his own inability to act.  So, Hamlet is being shown up by a player, whose apparent
ability to act and follow through on his emotional impulses is all for something
made-up, while Hamlet, with a real and important call to action can do
nothing.

And finally, the Gravediggers are also in the play
to provide a dramatic passage of time and to re-introduce Hamlet to the audience, who
has been absent from the play for a few scenes.  Time has passed, and the clowns help
show that to the audience by answering Hamlet's questions at Ophelia's
grave.