I don't know what to think of farming tasks. On one hand they can be completed instantly, however if we would change them, they would last 20/60 minutes, which is too long for such a minor task imo.
Hunter tasks should be added. There's quite a lot of variation in its content, so they wouldn't get as lackluster.
Thieving: I would have nothing against it.
Rune essence tasks would be fine for players with low mining, but they'd be quite annoying imo. I'd rather not have them.
Runecrafting: As Charr already mentioned, rc tasks should be different. Rune multiplication levels shouldn't count, because getting basic rune tasks at high levels is simply frustrating.
I do agree on Astral runes: this is also the place where rune ess mining comes in, because that combination is the only right way to make them.
The worst problem daily tasks currently have is the reward shop. I personally quit doing them as soon as double xp scrolls were removed. Don't get me wrong, auras can be useful, however they're not enough to keep the shop viable. I currently have no suggestions towards actual items that could be added though.
I like the task removal system idea, but Skill0wzer, the negative effect is unnecessary. You already lose a task if you choose to remove one. Since you get a maximum of 2-3 per day, I'd say it's quite significant. We could add a small cash cost to it though.