I have been a lurker for some time now, and must confess that I am a complete novice. Based on your description, I assume the following:
- neither you nor your wife are frequent travellers
- you want to maixmise any adantage possible on future travel

If these assumptions are correct, I would suggest the following:
- transfer these miles inot one account so that you may double them.
- create Delta skymiles accounts if they do not already exist (for a total of 48,000) miles.
- Transfer from account to its corresponding account from NW to DL
- In DL, transfer from one spouse's account to the other's

This way, you will have 96,000 miles in one account -- good for several tickets domestic, or a couple of tickets to Europe, or well on the way for a ticket to Asia.

If you are truly infrequent travellers, you are not interested in status, and are interested in maximising milegae for a future free ticket. If that is true, the cost of $0.01 per mile is cheaper than actually flying.