When I was teaching private and such, I tended to cover everything up anyways. Made the guys and gals fly by looking outside and look at the horizon rather than chasing the instruments. I think if you can fly, then every instrument you add later will just make you better.
If he is planning on getting an instrument rating and a commercial later, then maybe it wouldn't be a bad idea to add stuff.
The only reason why I like to have instrumentation is for getting caught in IFR conditions. But in helicopters we rather stay far away from them...
Other than that, I'm with G-Man. As long as you can finish your training legally by using another plane to finish your requirements, keep the plane vintage and stick in a hand held GPS.
(he might have to take the checkride in the other plane as well, not sure what the PTS says about VOR's, and flying headings, and demonstrating instrument flight)