Experience: If you are leveling any of your characters, the experience rewards for in-game holiday quests are usually huge. They scale with your level, so that they are worthwhile for level 7 or level 77. For the Midsummer Fire Festival, honoring flames gives a large amount of XP and desecrating flames gives twice as much. The ratio of experience gained to time spent is almost obscene.
Gold: Max level characters, as you know, get gold rewards instead of experience when completing quests. So the exorbitant XP rewards convert to large amounts of cash in return for completing holiday activities. If you need the extra gold, adding a little holiday fun to your playsession will help you raise some quickly.
Alts: For each holiday, I transport all of the alts I have any intention of ever leveling to the main event location. I then log into each one daily to complete the quests. I leveled every alt during Hallow's End by just doing the daily quests in Brill. And then I did it again in Bloodhoof Village for Noblegarden. Warning: Completing holidays on multiple characters accumulates a whole lot of event paraphernalia.
Exploration: WoW really rewards you for exploring their world. You get experience, fill out your map, garner achievements, etc. Completing holiday events like Midsummer and the Lunar Festival is a great opportunity to see more of the world and pick up these extra exploration benefits while you do it. Tip: Don't forget to pick up all of your flightpaths.
Goodies: If you are a collector, there really is no better way to get cool pets, costumes and props than the holidays. I just wish there were a separate bank tab solely for holiday stuff, so that I could have more space for everyday things.
Socializing: Impromptu groups thrown together for accomplishing or defending against holiday quests are a great way to meet new people. Whether you are looking for a new guild, recruiting for your own or just wanting to add to your friends list -- holiday gatherings introduce you to people on your server with similar schedules. Or you can join in events like our It came from the Blog activities solely to hang out with people with like interests. Even though gamers are often depicted as basement-dwelling hermits, we know that's not true... mostly. Even when we are soloing so much because of our restricted schedules, we still like having people to chat with.
Variety: I love leveling alts and I'll go back to enjoying Battlegrounds when patch 3.2 hits, but doing the same ol' thing every game session is the definition of a grind. Holidays add what I think is a necessary variety to WoW, keeping it fresh-ish, particularly in between expansions and major content patches. Semi-organized bar fights and reindeer rescues provide alternatives to collect a bunch of this and kill a whole lot of that.
Holidays enable you to spend your limited playtime doing something different while still advancing your character. As a casual player, I think they are always worth a try, even when they end up being kind of disappointing. But, of course, you choose your own fun and if they don't float your boat, then that's OK, too. Midsummer Fire Festival ends this weekend. Give it a try if you haven't already. Or not. It's not like I get a commission if you do. Regardless, I'm off to visit flames before they go away. Maybe I'll see you there.