Don't forget that in addition to the mechanical drawbacks of spellburn there are roleplaying drawbacks as well.
Or, the player could burn 8 points and find, oddly, that even though he got the bonus, he didn't lose the points. The next time it's most inconvenient, the wizard's patron shows up and says, "Ahem. About that 8 points...I'm here to collect now."
That definitely succeeds in making the game unpredictable. However, if rules don't work when the judge says they don't, it is no longer a game of rules; it is a game of judge fiat. Some groups can make that work, other groups can't.
Also, that particular version of judge fiat will only work if your gaming group is very stable. I have trouble getting a consistent group of players to show up; if they do show up and avoid computer games, I have trouble getting them to stick with characters and long-term campaigns.
If your players don't stick with the same campaign every week, a lot of these old-school techniques don't work.