You could try the mind-bogglingly simple approach of asking her to please not abuse the privilege. Or is that too rational between a husband and wife? 
You could require them to rotate the question-asking role.
You could, as others have suggested, adopt an overkill expression to mask your tells. Giggle maniacally when they use her information to help make a decision.
Or, just let them have the benefit, but make the problems more difficult.
A variant on the above, an agreement between you and your wife - she may use her ability to read you, but only if she bribes you. As consenting, even married, adults, I'm sure you can figure out a bribe appropriate for her assets....

You could require them to rotate the question-asking role.
You could, as others have suggested, adopt an overkill expression to mask your tells. Giggle maniacally when they use her information to help make a decision.
Or, just let them have the benefit, but make the problems more difficult.
A variant on the above, an agreement between you and your wife - she may use her ability to read you, but only if she bribes you. As consenting, even married, adults, I'm sure you can figure out a bribe appropriate for her assets....