Are the fire spells fuel, power link, detonate, and backdraft worth doing grizzleheim and wintertusk for? They seem kind of pointless except for backdraft for 1 in a million. Are these spells commonly used or just the ones you know but never use?
I can think of many uses for them all except power link, that's pretty pointless. Fuel gets used about as much as any school trap. Backdraft is like Supercharge, seems cool but rarely used except maybe farming certain bosses. Detonate is really only useful in a team situation where another fire cast a Hell Hound right before. There's also the lvl 75 minion. You can live just fine without all these spells, but there's always the question of what new spells they might add at higher levels that require knowing them. It's a choice you need to make, I prefer knowing all my spells personally, even if I almost never put them in my deck.
Backdraft is very useful when you get to higher level bosses. You can set up hits that end battles with one hit, greatly decreasing length of most boss battles.
Fuel can be a useful trap.
And I disagree with Seethe about Power Link. A boosted power link can actually do a fair amount of damage, while healing at the same time -- especially if it criticals. I use this frequently -- it is a great help when soloing, and is also useful for removing shields (especially if the enemy spams multiple shields) for larger hits to come.
I agree, though, that I like to know all my school spells, and to keep the pathways open for further spells to come.