According to the Recruit-a-Friend FAQ:
How can I earn the free 30-day credit?
For each friend or family member you refer who upgrades to a retail version of World of Warcraft and purchases 30 days of game time via subscription or game card, you will receive a credit for 30 days of free game play.
When will I earn this 30-day credit?
Your account will receive 30 days of free game play after an upgraded recruit's payment finalizes for their purchased game time.
Note: In cases where a recruit sets up a subscription plan, their payment will not initiate until after any game time they currently have expires. This includes the free 30 days of game time that comes with the retail version of World of Warcraft.
There are many daily quests one can choose from in a day to reach the 25 quest limit per day. The rewards from these quests always include gold, but sometimes include other things such as mounts, pets, reputation, gear, achievements, and titles. As for "worthwhile" dailies, it sounds like that would include any that give you something other than money for you. You would have to do some research on each individual faction, but most factions have dailies you can complete to grind to exalted (but not all). Some of these are very similar, if not exactly the same, as Tol Barad dailies. You do dailies, gain reputation, then you can buy things from their quartermaster through money or other currencies. Some of the ones that I enjoyed doing, or had a rewarding experience from included the following:
Note: The descriptions are my own; take them with a grain of salt.
Tol Barad(lvl 85) - As you mentioned, two mounts, a pet, and various toys.
Molten Front(85) - Pets, toys, lots of achievements, and ultimately a title and mount ("the Flamebreaker" and a Flaming Hippogryph). This is the long and arduous quest chain that leads the player to the Firelands and explains the situation. Very entertaining and rewarding.
Argent Tournament(80) - Each daily rewards you with crusader tokens that you can use to buy a huge number of things including, but not limited to mounts, pets, tabards, and toys. Reputation can be gained toward multiple factions through this chain. You also receive titles for unlocking each part of the line ("of [city]"), as well as the "Crusader" title upon unlocking every part. This line is dynamic to a point, but takes a very long time to gather enough tokens to buy all the cool things.
Netherwing(70) - Rewards one of my favorite type of flying mounts, was an epic grind back in the day. Also had very entertaining and challenging racing quests as you increased reputation.
Shattered Sun Offensive(70) - The first phased daily quest line. Was interactive when it was relevant, since new parts of the Sunwell raid weren't unlocked on your server until the players on that server collectively did enough dailies. Probably boring now. Rewards a cool tabard and title ("of the Shattered Sun").
Sha'tari Skyguard(70) - Not very engaging past the first few days, takes a long time; rewards include nether ray mounts and a multitude of achievements.
Wintersaber Trainers(60) - A grind of absolutely epic proportion when it first came out (wasn't in a daily format). Has since been re-tooled to account for complaints about inaccessibility, and is more of a daily-type experience that doesn't take too long to complete. Since I did the original version, I'm not entirely sure what it's like now. Rewards a very sleek looking Wintersaber mount.
Darkmoon Faire(any) - A new (refurbished) event that shows up once a month. Rewards include mounts, pets, and cosmetic armor that doesn't exist anywhere else in the game (anymore). Earning tickets from this takes a while since it isn't always around.
Each of these reward reputation and an achievement or two. This is not a complete list of dailies that have good rewards. There are most certainly others that fit in the same category, but I don't feel like listing every single one. There are a few that are just a simple daily that is unlocked through main quests that have a chance to drop something cool. I'll let you discover these, as well as the multitude of other options there are. It is a role-playing game, after all!
Best Answer
In legacy raids you have one shot at the mount per lockout.
You can clear the raid once per lockout, regardless of its difficulty (since you're able to change the difficulty while you're in the raid instance).
An exception are raids with the raid finder difficulty enabled (Dragon Soul and later). You can talk to the raid's npc and clear the raid finder difficulty as well. For Dragon Soul that guy stands right before the entrance, but since you can't loot the Experiment 12B on this difficulty it doesn't help you anyway.