Closing Apps and RAM on iOS

I know lots of people, myself included, who are quite particular about regularly killing apps running in the background after using them. The whole process of double-clicking the home button, pressing and holding the apps located on multitasking bar, and hitting the red delete button to completely quit them, has been a ritual at the end of the day. Obsessive compulsive, you think?

Given that the iPhone 4/4S has 512mb of RAM:

a. is it really necessary to kill all the apps running in the multitasking bar?

b. will killing these apps bring about improvements in speed etc?

c. will keeping these apps open in the task bar use more battery power?

c. does using a "RAM clearer" app (that free's up used RAM) benefit or harm the device's processes?

I have noticed that free RAM is always biggest after a fresh reboot, and although I've completely killed some apps, the RAM almost never goes back to that same state until the next reboot.

I have enjoyed reading and posting on The Verge, it seems like people are really passionate, knowledgeable and engaged in the groups they are part of (Apple Core. Can't say for other forums on here yet)

Oh, and I love how bashing and attitude are almost (still) nonexistent! :-P