Wait... HW1, I kind of get. It's sort of dated, and there were some minor issues (fixed in Cataclysm).
But... does "Homeworld 2" mean "Cataclysm" or the actual HW2? Cataclysm looks like HW1 with some of the bugs ironed out (so it could use an HD remake), but HW2 didn't look bad at all! It's not even all that dated.
If there's any reason to re-release HW2 is to fix all the balance issues which that game had. Most notably the really really shitty "dynamic difficulty".
Than again, the story of HW2 wasn't the best either - I far more liked HW1 and Cataclysm in that regard.