I felt compelled to create an account after reading through this entire thread and I offer a fresh perspective.
First off I am from Simi, and work in Calabasas off of Las Virgenes. I don't know Matt personally but grew up in all of the surrounding areas. The In N Out referenced (on Stearns) is a very common hangout spot—it's just about the only hangout spot as there is nothing to do in Simi.
Oftentimes as a young adult(highschool/college aged with free summers) at night it wouldn't be uncommon for friends to go the helicopter pad (up Tapo Street) to hang out drink, smoke pot, etc. It was a short hike up an access road at the top of a hill. Pretty harmless fun. I don't know Rosas Point where Matt disappeared but it reminded me of the helicopter pad. Combined with the grafiti and what others said, it surely was a hangout spot for youth to drink/do drugs/grafiti etc. and was very well known. The main difference is that Rosas Point looked almost impossible to access, especially at night and with a small car! I find it hard to believe this kid would have driven out there all alone, in pitch black darkness, on a narrow hiking trail not meant for driving.
But he must have, and there must have been no one else at Rosas Point that night.
His keys/wallet/personal belongings are missing which tells me they are still on his person. Matt had a history of "going out and getting away" in Malibu. Maybe this was a spot where he would go to reflect and think. Or maybe he had never been to this particular spot before, GPS'd it, got to a 'dirt road' (the hiking trail) and continued to cautiously proceed over the bumps and gravel until he got to Rosas Point. He could have carefully gotten out of his car checked out the view and reflected for a bit. Then he could have gone back to his car and slipped and fallen down the steep mountain to his doom. He'd scream cries for help for hours which would echo off of the quiet night mountains. Local residents could hear the bellowing screams. Law enforcement's response time was slow but this area is pretty remote and takes a while to navigate, and the call itself would have been lower priority with seemingly less urgency (hindsight tells us different obviously). The police also would have responded to the house that made the call. The trail and Rosas point itself are VERY remote. So they could have heard the screams from quite a distance away. They too were unable to locate Matthew's position in the pitch black, hard to navigate terrain. The time ticked and unfortunately Matthew could have succumb to his wounds.
That story makes sense if he was alone and no one else was at Rosas point, but what if he wasn't alone or there were others at Rosas Point?
We need to know where/when the spray paint came from.
Was it something law enforcement, or someone else put on after they found his car?
Or did the spray painting take place that night by other individuals?
That shouldn't be hard to obtain information and then opens up the story to a lot more speculation about other suspects, random people that were there that could have harmed him, etc.
I wonder if the gate was kept locked if he would have ever gone up there.