I am not sure what BC will do to this, but fishing is one of the super money makers of the game, stonescale eels rock!!!!!!!.
Some of my points on doubble gathering.
You will make copious ammounts of money, I mean truely disturbing money. Even on a brand new server with a weak economy, there is money everyplace. Not only are you selling your stuff for money, you are not spending money leveling a trade. For example even with a main feeding them a tradeskill cost about 40-80 gold to level to 300, and thats a low apromoation. If you think of every time you bought a item on the AH to level alchemy, of every recipe you bough, of each level uncap, of every time you made a item for a buddy free of charge, of every time you gave up a good drop to get a recipe that is totaly awsum(thinking flasks) you would see that having a job cost much much more than just the visiable cost. My point? well you make money as well as save money by not sinking it in to a trade.
The drawback? Well I may be a rare one but what do you need Gold for? pretty much one thing, Mounts. I leveled at least a dozzen toons to the late 50's and 6 all the way to 60, I have purhased 12 normal mounts and 4 epic mounts. While I had a hard time on my first mount the rest were eazy, all I had to do was be aware of it. Doubble gathering is a fast and eazy way to make money but alchemy can pay off well too, every 48 hrs is a free 5 gold for a transmute(24 hrs if you have a sweet elemental transmute) and stuff like flasks sell like hotcakes, for big bux.
The bottom line to me is that while doubble gathering is the best way to make money(that you can then use to buy stuff), but not the only way, I have never been in a pinch where I could not get what I wanted(remember I also never played a exclusive Melee toon, so stuff like cursader was never on my objective lists)if you like having potions, stay with alchemy, If you think you will never see 100 gold for you mount, then be a gather. IMHO the most important part is to have fun with what you are doing!