Lived on Oahu from 2010 to 12. Local TV station played reruns of the original every day around 5 pm. It made my time there wonderful!
The Anderson Estate where Robin's Nest was located was for sale a few years ago for around $12.5 million. Purchased for just over $8m. It has now been torn down for a development. Not cool.
Pahonu (aka Robin's Nest) torn down!
4/14/2018 - Sad news for Magnum P.I. fans this week. The building structures of Pahonu, the property in Waimanalo that was used as the exterior filming location for Robin's Nest (and used in nearly every episode), have been torn down to make way for a new, unknown development project. The demolition occured without any kind of historic preservation review, which wasn't required because of a 2015 state law change that excluded privately-owned, single-family detached dwelling units from historic preservation review unless they are "listed on the state or national registers; nominated for the register; or located in a historic district." The estate was purchased by Marty Nesbitt (close friend of Barack Obama) in 2015 for $8.7 million. The City & County of Honolulu Department of Planning and Permitting (DPP) issued the demolition permit last week. The 8,900 square feet Spanish Colonial Revival-style main house was built in 1933 and was designed by architect Louis Davis, who was a prominent architect of the 1920's and 30's. The future plans for the property are currently unknown. Here's an aerial view of the destruction. 
For all things Magnum:
Magnum Mania! For All Things Magnum P.I.
You can even get repros of his Aloha shirts