I do not think that people should go on deleting their contacts. i think that people are being hacked just from using your email from every day little things like using your email at the store or purchasing something online. I think the only way to avoid being hacked is to stop putting your email or everywhere and to have a well protected password.
No, you should not begin deleting your friends from your contacts list in order to avoid being hacked. If your friends are truly your friends, they pose no risk to your account. As long as people stop inviting strangers to join their social circle, the risk of hacking will decrease dramatically.
Gmail account hacking, although rare in my opinion, is not done by your friends. It is done by expert hackers that are paid to hack into your accounts by companies or scam artists. Therefore, no, I do not believe that you should delete your friends to stop the hacking of your account. Having friends in a contact list is one of the features of having an email account, at least a GOOD email account. So if you are going to delete your friends, just get another email account anyway.
I don't really see how that would help. Just don't be stupid and click on spam emails. They are usually very obvious. I haven't had any issues, that I know of, with anyone spamming me. I just set all my filters to weed out what I don't want and I don't click on links unless I know the site is legit.