Dentist wants to replace existing veneers w/opaque to prevent show through. I prefer translucent. (photo)

Translucent veneers do indeed look more natural than opaque. Your dentist should be able the prep your teeth more, allowing for thicker veneers that will prevent show through without being bulky. I always recommend okaying your restorations before having them permanently bonded. That way, any necessary changes to shade, shape and fit can easily be made.  I hope this helps.  Follow me for more questions and answers.

Choosing veneer opaqueness depends on the darkness of the tooth structure underneath the veneer.  More translucent veneers look more natural but let more color through and more opaque veneers look less natural but block more color.  When your dentist prepares your teeth for the veneers, they should be taking a shade match of your teeth underneath with a photo and sending it to the lab.  Then the lab can look at your shade underneath and the final shade you are trying to achieve after you are all done and choose the appropriate ingot opaqueness for the veneers that will be a good balance between opaqueness and translucency.  The thickness of the veneer will also affect the color transmission.  Your dentist should try on the veneers with try-in cement paste for you to see the final color prior to bonding to make sure that you are happy with the final look.