Instawire fees over Bitcoin Central fees and their respective KYC policies?
You got the answer in the question : the fees are higher on Instawire because it is a service, not an exchange.

The fact is also that (until Bitcoin is legally considered a currency) sales of Bitcoins are subjected to European VAT which instantly adds 19.6% to the price. (If Paymium buys a Bitcoin at 10 EUR, it must sell it at 11.96 EUR to start breaking even).

There is no legal requirement to do KYC on Instawire as no funds are held on behalf of users, sometimes documents might be requested, but when they are it is for fraud-prevention purposes, not KYC. The 100€ limit is also a fraud-prevention measure.