Englishman,
If you are feeling that your wife is now immature and shallow I would suggest you think about the following points.
1. Do you bring up topics that she can see as a criticism of her? If so I would assume she just turns off rather than have a deep discussion in which she feels criticized. (Even if you do not mean it in that way)
2. Perhaps she needs to talk about her day which includes many “shallow” things like diapers and laundry etc. If that is the case try really listening to her before you have “deep” talk with her.
3. Perhaps at the end of the day she is just too tired to talk about those deep issues that you used to talk about when you were dating.
If the above does not help you remember that a spouse is not perfect and cannot fill all our needs. Most people need other people beside their spouse to fill ALL their needs. So if you have Shalom Bayis and nothing major is wrong, find your intellectual needs elsewhere.
Good luck!