I havent really looked into how this darkcoin things works but it sounds that purely mathematically it would be profitable to buy into darkcoin in general if the price is expected to rise in the future.

If one buys enough to become a masternode it would then be profitable if the price of darcoins:
would go up
or stay the same
or even go down but the avg decrease would be less than the daily profit from beeing a masternode whether that will be 0.6% or lower in the future.

So the biggest factor would be to analyse where the price of darkcoins would go in the short and long perspective and secondarily if one buys enough darkcoins to possibly becomes a masternode then there would also be a slight bonus for that to.