Seems to be a little too much paranoid to want to use HTTPS for everything.
The difference is, HTTP is plain text, who anyone can see, HTTPS is encrypted and nobody can see it. While it's true that HTTP can be seen by anyone with a proper setup, that don't means that you'll be actually spied on.
For some sites, HTTPS is a must (banks, PayPal, maybe emails, or everything that must be kept private), but for general browsing is just overkill and slower. For example, does it matters if anyone can see what you search in Google? Or does it matters if anyone can see what you wrote at SF? Or some bog you may be viewing? Most likely not. But if you're sending credit card info, you'll want encryption. Just think where you really need extra security and where it adds nothing.
And after all, using HTTPS or not is a website decision, not yours (if the site supports it or not), as you can't force it upon any site you want. Just check for it if you really need it, and keep away from sites that require it but don't offer it.