What would be the source of this "future wealth" ?
Validity is going to depend hugely on the circumstances at the time. Two examples off the top of my head:
- You get married, are given a lump sum from family on the wedding day, consummate it and then she immediately files for divorce, then sure - money grabbing 'ho deserves nothing.
- You get married, have a few children, build a successful business while she looks after them and divorce happens as she never sees you and wants a career back, then yes - you hand over a big pile to the hugely supportive wife and also pay maintenance for the children until they are old enough to stand on their own.
Even Dowie's "reassuringly expensive" solicitor isn't going to save you if the other side's legal team can argue well when it comes to the settlement. Decide what's more important to you, the person you are going to marry or the money you don't yet have.