I might actually put a second in the spellbook now, but I'm not sure. In my initial assessment I figured there was no way it would get dispelled because of cost. It still seems unlikely, but now I'm not as sure.
I've been toying with having two in my FM spellbook... not only is there an off chance of one getting dispelled, but I wonder if sometimes (very rarely) it might be worthwhile to voluntarily replace it.
The only time I see this as a possibility, is when the FF is beat down the previous turn, and when facing two to four high-effect creatures and no little ones. Then I wonder if it wouldn't be worth not paying upkeep for the one use per turn... and then bring out another copy as soon as you can the next turn, gaining two more uses that turn.
It's just a question of whether the mana cost (discounted for not paying upkeep) and loss of an action is worth it. Right now I'm guessing that you would have to be pretty desperate in terms of life left while at the same time having an overabundance of mana available... conditions that likely won't happen at the same time.
Here's a question though: Can someone remove a spell that he or she cast earlier at any time (or is failure to pay upkeep the only way to do this)? If so, then I wonder if it isn't good to remove the first one when smaller creatures have knocked it down to zero tokens to get another fresh one out (presuming enough mana, etc.