Yeah, that's the only drawback to VGPMX. Back a few years ago it had a $3,000 minimum but so many people bought into it they had to close the fund to prevent it from becoming too big. When they reopened it about two years ago, it had a $10,000 minimum to stem the inflows.
There's an ETF that basically tracks the platinum miners index called PLTM but I don't know much about it. Perhaps if that seems appealing to you then that might be the best route to take.
Cuimhnigh orm, a Dhia, le haghaidh maith.