I would either sell it or use it. If I had the space and location, I might even consider using it as a display piece. You can keep it in the box and hope the value of it goes up before you one day do sell it, but in reality, it probably will not gain a whole lot more value than it has now and may even regress if real value due to inflation.
Someone might pay $1000 for it today, but in 1985 money, that is about $400 which is probably what it was sold for new in 1985. So, it really has not increased in value at all over the last 35 years. Keeping it another 10 years in the box probably won't make an appreciable difference.