The idea behind a flex fan is that the fan blades keep a tight curve at low RPM to increase the amount of air pulled by the blades, but at higher RPM centrifugal force causes the flexible fan blades to flatten out, thus pulling less air and reducing drag. The problem is that sometimes the plastic fan blades get stress fractures from flexing or get other damage from road debris kicked up or tools dropped or the blades just fail. The blades then fly apart at whatever RPM they are turning, potentially causing damage or injury to the vehicle or nearby people.
If you are looking for an easy way to reduce drag caused by a fixed blade fan, the best bet is to install a factory clutch fan. If you want the latest whiz-bang product then you go for the electric fan, but, to do it right, it is a somewhat involved installation. Mount the fan, mount the temp sensor, run the wiring, run a failsafe switch for if or when the relay or temp sensor fails, make sure the alternator has enough output at idle to power the fan, etc... Much easier to just bolt on a clutch fan.
Synthetic oil is a good upgrade, the PCV is a regular maintenance part that needs replacing, brakes are good, and I don't think much of K&N on a street vehicle. A Napa Gold filter flows just about the same and the difference isn't enough to notice on the street.
