The only difference between the gold edition and the DLC pack is that the gold edition also includes the palomino horse. As a long-time player you may already have that or may have mounts you prefer anyway.
I don't know what the benefits of linking your account to Steam are (I avoid using Steam unless I have to), but I would have thought there would be a way to link your account without buying another copy.
Dont buy via steam if you want to support ESO
Steam gets a share of the $$$ so ZOS gets less....