I've got 108,000 miles on mine.  There is no oil consumption to speak of...
(coolant, some.  But no oil comsumption so far...)

 > The the things that make me hesitant are:
 > -  it's loud from the outside at idle ( a lot louder that I recall my old '80
 > Rabbit diesel being) which might indicate a problem (?);  

It should not be all that loud...

 > 
 > -  it blows a cloud of black smoke upon heavy/fast acceleration  (which is
 > clearly visible from the rear view mirror);
 > o  Remember this engine is a LOT more loaded than a Rabbit under acceleration.
 >  Could also be injection pump is not timed or mixture adjsutment is off trying
 > to get more powere.
 > 

This is not a good indicator.  My '82 diesel puts out hardly any smoke
even as I floor the pedal, at any rpm / any speed.  We've had the
valves adjusted regularly at every 15,000 miles, and if the dealer is
to be believed, not adjusting the valves at regular intervals is one
cause of the black diesel smoke syndrome...

 > - it's a slug -very slow acceleration and top speed of what appeared to be
 > 60mph.
I can cruise at 65/67 mph on level road no problem.  I thought this
was not good, but the westy never drove any faster except downhills --
even when it was a young puppy.

In all, The black smoke is probably the thing you wanna be most
careful about.  Also, check the engine from top -- in mine the coolant
was forming a small pool at a depression on the engine block right
under the rim of the cylinder head.  This mostly went away recently,
after I used that Bar's Leaks stuff on it.

Good luck,
Cetin