If you think you can make it to 21st level on your current Will saves, pick up Manyshot or Shot on the Run. Once you're epic, you can pick up the Dexterous Will feat, which allows you to swap your Dex modifier for your Wis modifier on Will saves. (Boo-ya!)
i've thought about combat reflexes, but our fights tend to be static. one of the fighters is terrified of AoO and has become skilled at turning combat into line fighting.
a different angle...for next level...how do you feel about opportunist or crippling strike?