personally having owned both pre and post face lift models and a GTA I much prefer the living environment of the face lift interior, its a much nicer more sophisticated place to be.
the GTA had the bose stereo in her as well which is also a nice enough sounding bit of kit, esp once I'd got my ipod adapter on there.
i'd certainly take the 2.4jtd over the 1.8ts as well. I've only driven the mjet 2.4 mind but its a very good motor and very smooth. drives nice enough as well and no doubt better mpg.
the thing you need to do is hold out for the right car, if you want a 2.4jtd with leather and face lift interior then wait for it, no good wasting your money then throwing more money at it trying to make it what you want it to be.
don't be afraid of the 1.9jtdm engines either. I originally get out for a facelift 2.4jtdm when I bought my latest alfa and ended up coming home with a very nice 156 1.9jtdm sports after about 6 weeks of looking at motors. was rather impressed with the way she drove!
1999 156 1.8TS Sport Pack 3
2001 166 3.0 V6 24V Super
2003 156 GTA 3.2 V6 24V
2005 156 1.9 JTDM-Jet Sport
2008 159 1.9 JTDM Lusso
1997 GTV 2.0TS Lusso
2001 147 1.6TS Lusso