I've thought about this same subject for a few years now. Well actually for a few decades, ever since I saw "The Treasure of the Seirra Madre" and discovered a few treasure magazines in my dad's collection of True West and Frontier Times. I got the impression early on that alot of work was involved and not much romance. I pretty much lost intrest when puberty hit.
I've been giving all this alot of thought recently. I'm more of a scrounger than anything and to me anything I find that I can either trade or make a buck off of is considered a treasure. Most of the time I come across something intresting I will either keep it or give it to someone who wants it more than me. That's the hobby aspect of it for me.
If I was going to try making a living at it, I'd consider salvage and recycling as an option. Hitting the flea markets, garage sales and estate auctions would be a good way to procure items for a profitable resale later. This could allow you to have a somewhat steady income to live on and an oppunity to find some good treasure to boot.
I just don't see anyone making it as THer without being able to take advantage of every oppunity that presents itself. You might coin shoot an old playground one day and dumpter dive the next. If you happen to be hunting caches on an old homestead and come across the site of the old outhouse or garbage dump, well get you digging tools out and hunt for bottles.
One time I was hunting arrowheads and found a fossile bed loaded with shells from some large species of sea snail. Not really worth much but I dug out a few pounds of them anyway.
Now suppose you succesed in finding your loot, next you have to find a market for it. That is an area that worries me the most since I have no experience here. If the economy is down like it is now, the market for antiques and relics will be down. Collectors will be less willing to buy stuff. There should be a tutorial on how to dispose of your goods, if there isn't one laready.
Anyway that's my 2 cents.
good luck with whatever you choose to do 
