remodel & upgrade or buy an upgraded plane?

Hi,

I have a 1967 m20e super 21. It has little for instrumentation and
the radio stack is pretty weak. It certainly isn't near IFR. The
interior is original and the paint is 5/10. It'll cruise at 130kts
2200 rpm and 23"

I'm looking for opinions on whether to upgrade and have a sharp, but
old plane... or should I just wait a couple more years and purchase a
newer plane that would meet my requirement and would potentially be
faster?

I'm just wondering about the resale. If I had an old house and built
a swimming pool outside for 20,000$... if I went to sell the whole
place I'd never get that money back out of the pool. Is it the same
with airplanes?

Any advice would be appreciated.

Thanks,

-Dico