I had a chance to fly that Harvard with a non-standard glass display, while doing manoevres that you wouldn't normally have your head in the cockpit doing.
The research they do leads to new/updated aircraft, but not necessarily directly (ie they're more about research than R&D). They identify/confirm in an airborne environment what new ideas work well and what don't. Much of their work is done for other agencies, but I'm not aware whether or not the Harvard was used in that way.
As far as using something as old as the Harvard as a research aircraft, the research is on the display software, so any aircraft that allows the desired flight envelope is a good aircraft.