I'm even more of a latecomer (1990s!!) and have seen a couple of mods to the Mk 103 over that time, notably a reprofiled compressor a few years back. Something to do with squeezing a bit more medium-level performance out of the old girl. There has often been talk of fitting the ex-F3 Mk 104s for the same reason, but I must confess to being ignorant of the technical issues involved.
The most notable thing for me over the 20-odd years I've been associated with the jet is the ingenuity with which the original systems architecture (focussed on low-level TFR strike ops) has been modified and tweaked to the point that the aircraft remains at the forefront of modern conflicts. I don't consider the GR1-GR4 upgrade as much of a step change as was Jag GR1-GR3; in fact the OEM software on early GR4s was, in some ways, a backwards step from the final iteration of GR1. Once the in-service software team got properly stuck into the GR4 we have not looked back; much of the GR4's increased capability has been added piecemeal over the years through small hardware and software mods since the mid-life update was completed. Overall quite a good bit of work.