Legendary items already make up most of the gold you make even if you pick up everything and sell anything you find on the AH. Doubling it will just make it worse. AH is already spammed with legendary items.
Not really. The AH is spammed with a lot of bad legendaries because legendaries are sufficiently rare that everyone thinks that legendaries are OMG AMAZING!!!!11! What will happen is that more legendaries drop (twice as many, in fact) which will cause the bad rolls to be salvaged (as opposed to be spammed on the AH), the average drops (currently in the 5-10m pricing range) to drop down to maybe 2-4mil (like the bad ones are now) and the high-end ones will just stay as expensive as they are. After the patch a 900 echoing Fury might simply be unsellable while right now you can probably fetch 2-3m for it.
No matter what the drop chances are, there will ALWAYS be a 5% best items, which will always be super expensive. If you're not getting a lot of 10m+ drops right now, you won't be getting a lot more after the patch. Yes, you're going to find more and better gear, but so will everyone else. Somoenone might be looking for boots with 100 int 100 vit 12% ms now, but after the patch that person will probably add 70 resall to that list and he will expect to pay the same price.
The value of an item is a function of how hard it is to obtain and nothing else, really. In the end, playing 50+ hours a week will always get you better and more drops than doing a run a day. How hard is this to understand?