The directions below worked to get all my i-devices back to being recognized and syncing over wifi (Mavericks/iTunes 11.1.3). 😀 One additional step I added was in Airport Utility changed my internet options to Configure IPv6 from link-local only to "Automatically"...found in Internet Tab, select Internet Options...
From another discussion thread on the same topic:
RKCOJOHN
Folks, you could try this - it worked a charm (so far) for me.
Go into System Preferences / Network.
Choose your ethernet and/or wifi connection.
Go to "Advanced". If you're working on wifi settings, you'll need to pick the TCP/IP tab from the next window. If you're working on Ethernet settings, it should default to the TCP/IP tab.
If IPV6 is set to "off", change it to "Automatically" or put in "Manual" settings as you prefer. Apply the changes. Close iTunes & restart the Mac. Open iTunes once you're restarted and, if you're like me, your wifi sync devices will show up very quickly in the side bar.
Sync still seems to pause for a while on last step, but it has not yet failed on iPad, iPad 2, iPhone 3GS, 4S & 5.
Steve's earlier post led me down this path and prompted me to check this. I have a vague recollection that I forced IPV6 to "off" to overcome problems with prior upgrades to OS X and/or iTunes.
Hope your frustration comes to an end as, hopefully, mine has. I'm optimistic because I've been playing around for 2 days with variations of all the suggestions on this discussion. I'll post back if, as for some others, this fix only works temporarily. Good luck!