Alfa dealers expensive?  Too damn right AND they'll only do whats on the
*menu*.  Maybe you can find someone here,
http://www.aroc-uk.com/suppliersandservices.htm  What happens to the
temperature when you drive around with the aircon on full heat?  If it comes
down by 10'C or thereabouts, I'd say you have a flow problem in your cooling
system.  Could mean radiator, thermostat or water pump or all three.  My
guess would be radiator.  3/4 on the gauge is not normal for regular
driving.  Not sure what the thermostat is rated at on the JTS, but I guess
it's probably 87'C as the V6, so your temp should hang around the 1/2 mark
once the engine is warmed up.  It's not covered in the service, and they'll
charge you to diagnose it.  Don't push your luck with it.  A new radiator is
around £100 quid for the part, and up to 2 hours labour to fit.  Other than
that, another thing to watch out for, you're probably due new spark plugs,
if your schedule is the same as the V6 it won't be listed in the book.  You
should get it done anyway.

Someone will be along soon to say "timing belt".  The current recommendation
is around every 36k, AFAIK.  Something to think about.

Somewhere else to peruse, http://www.alfa156.net

Rgds

Stuart