I believe that's a good point. I think all semi-auto HK rifles/mp5 types quantity wise never met demand and raised in value/price.Well if you want an MP5, you can spend $2K on a clone, or you can spend another G and get the real thing. Neither will make you breakfast but one will stir the soul more than the other. Depends on what you want and what you can live with.
Further more, a clone MAY go up in value over time just as all guns. But with an HK it's basically a guarantee that it will.