How "low interest" is the heloc? If it is above 4% I would probably put half toward that and the other half in a mutual fund for a future move. We plan to move in 4-ish years so we are saving for an out-of-state move and a down payment on a new house once we do move.
Combine with my current vacation house savings fund and maybe consider if I had enough for the downpayment. I also consider that an investment property, so it would, in my mind, qualify as an investment.
As long as you still had equity in the house, I wouldn't be in a huge hurry to pay off the heloc over investing.