how do I restore *only* contacts to iPhone 4 via iTunes?

You cannot choose.

All or nothing.

You should be syncing your contacts to your computer regularly. Just sync them back.

I guess this is what you could do if someone you know could recover iPhone contacts:-

1. Get an iPhone and take a backup of the same on your system - use iTunes to do that;

2. Now (this is really critical and follow it at your own risk) log into your iCloud account on the phone and restore that phone while pointing to the iCloud backup. In this was you will have all of the iCloud data in that phone;

3. Now use another computer (or at least another user account on the same computer) to take a backup of the phone with your data - don't use the same account as everytime iTunes takes a backup of your phone, it overwrites the previous one. So you risk a chance of loosing the data which originally came with the phone;

4. Get an iPhone Data Recovery software and install it on the computer which has your data backed up.

I hope this will help you!

Recovering iCloud contacts, calendars, and bookmarks from an iTunes backup of an iOS device