If you do a lot of instances, or farm a lot of instances, disenchanting can be a good source of shards. And shards tend to sell well, depending on the type of shard of course. But if you spend most of your time soloing then I doubt disenchanting will be nearly as useful.
If you are only looking to make money, take up skinning or herbalism. While you can make some good money on certain crafted items, and enchants, it takes a lot of reputation work and/or lucky rolls in high end instances to get the good patterns. Skinning provides good stead income from mobs you’re killing anyway. Herbalism takes more hunting than skinning, but you should be used to that with mining. But many of the higher end herbs sell for a gold a piece, that’s 20 gold per stack. At least on my server.
If you enjoy production professions then go for it. Invest the time for good reputation with the right groups and you’ll eventually be able to make some nice stuff. And possibly make some very nice money. But for decent income without the reputation work two gathering skills are the way to go, at least in my opinion.