@Ross at Play
My conclusion is that the cliche would need to carry some connotation, beyond that of possible literal alternatives, which makes it a perfect fit for the what the author needs.
Or, to put it a slightly different way, most authors could probably rephrase the sentiment in an entirely new way, but what precisely would be post by doing so. In this case, you'd lose the entire 'this scheme is so uncertain, it's as fragile as walking on eggshells' implication, which you'd never even notice on a first read. That kind of double meaning is hard to capture, especially in so concise of phrasing, but it makes for a decent test.
On the other hand, no one will ever become good at turning a phrase, if they don't push themselves, and thereby gain the necessary experience. So don't take the easy way out, push yourself to come up with alternatives, see which work and which don't, and build on your strengths going forward. But if you keep relying on cliches, you'll never become adept at creating your own turns of phrase.
That's another reason for my 'stick to one character'. If you have one character who keeps using standard cliches, and another who always counters with his own take on it, you can develop a nice back and forth, where readers will see the one phrase, accept it for what it is, but then look to the other character to see whether he can one-up him. Thus it becomes an expected competition between the two characters. They might not all be winners, but if it helps develop the characters, and the readers get caught up in the competition, then the verbal sparing speaks louder than any single cliche.
Now, I wouldn't do that all the time, but doing if for a single story, between two characters, you should come away with a really good feel for you potential at create alternative analogies. If it doesn't pan out, then it's no great loss, but if it turns out that you have a knack for it, stick with it, and soon you'll be sparing with the best of them.
As I've said before, I've always dreamed of being a great wordsmith, able to phrase things beautifully. Agatha Christy's books were almost pure schlock, but her phrasing for her summaries were classics—everyone. Those 'new cliches' can carry a LOT of dead wood, so it's worth developing.