We can but...
At the point the query makes it to your server it's already too late. Your server will waste its resources trying to do something with the packets and the requests. Even if you have something like
iptables drop all connections it's still going to use up all of the bandwidth on the server inbound. Redirecting all traffic someplace else eats up your outbound bandwidth and propagates the network failure between your server and the now new target.
It's a network infrastructure issue. Not a server issue (unless it's an open recursive resolver). The traffic needs to be handled (killed) further up the pipe. Here's a CERT advisory from March 23rd.
Unfortunately, due to the overwhelming traffic volume that can be
produced by one of these attacks, there is often little that the
victim can do to counter a large-scale DNS amplification-based
distributed denial-of-service attack. While the only effective means
of eliminating this type of attack is to eliminate open recursive
resolvers, this requires a large-scale effort by numerous parties.
Source IP Verfication: Because the DNS queries being sent by the attacker-controlled clients must have a source address spoofed to
appear as the victim’s system, the first step to reducing the
effectiveness of DNS amplification is for Internet Service Providers
to deny any DNS traffic with spoofed addresses.