i say go for it....350 is ok, per replacement is 70. So the K & N filter will last you at least 7 times the normal filter and in addition it will give you better airflow. Yet you can wash it to clean it until the filter element wears out.
I have K & N fitted on my wira. Been using it till now, still in good condition. Saved me lots of $$$$$$$. do the math lah.