The G4 is 17 years old & is said to have the highest number of hours for the type. That seems to suggest that we as a country need more than one medium-long haul aircraft. On long haul flights it can take a full load of pax but is very restricted on baggage load.
The LJ is only suitable for short-medium haul flights, eg DUB-BRU.
The KA is even less suitable than the LJ & is much slower. However, it carries out a lot of other roles for the Air Corps, eg Twin Engine Conversion. It's 28 years old !
All 3 have performed well for the IAC over the years & have been excellent value for money.
Replacing the G4 has been on the cards for some years. Not doing so appears to be more to do with public perception & the willingness of non-government parties to slag off any government that considers spending the required money. Both the Boeing BBJ & Airbus 319 have been considered & both would be better value (cheaper to buy & operate) than a new Gulfstream. But they are larger, media & oposition parties seem to view that as "the boys splashing out on a big new toy".
& that's my two cents worth !
Regards,
Joe