I will not approach your questions head-on. Instead, I will explain a bit so that you will understand the whole Google SSL thing better. Here we go.
A fair majority of all of the metrics that dictate performance in the SERPs are domain related- meaning that in the database, the metric is relationally linked to the domain and not to a page or other site element. Well over half of these metrics are within the trust realm. In trust networks, not always having anything to do with communications networks, trusted entities can trust each other using recognized signatures and a known challenge and response pattern. SSL is the only such trust signature scheme on the web. The reason for this is simple. The Internet is a network founded upon trust and openness. SSL adds one measure of trust in a network not designed to trust. Therefore, any site that has a valid SSL certificate gets a gold star next to it's domain name and any site that has a high quality SSL certificate issuer gets a higher grade than one that does not.
End of story. Sorta.
It is only the fact that a site has a certificate and the quality of that certificate that is important. However, as Google tends to do from time to time, it wants to force it's will upon the Internet for our own good. Granted, Google thinks that we would all be better off if web traffic was secure and cannot be eaves dropped upon. While in part they are right, Google is not in the position to write the rules. Their proverbial wrists have been slapped a few times and they are a bit shy of Mother Superior. It is Google's opinion that you should only serve content up with encryption, however, it is also your right not to and you should not be punished as a result. And remember that not all content and content readers really need to be protected this way.
So what does this mean?
It means that if you have a valid certificate from a high quality issuer, and Google can see that by your offering content via SSL, then Google can and will trust you a bit more. It is a domain trust metric. Nothing more. Nothing less. A gold star and a grade. How you serve your content is up to you as long as Google can see that you have a certificate and that it is valid and good.
Lastly, for future readers, does this mean your site needs SSL? No! Absolutely not! The effect of just one trust metric is small. It is the total trust score that a domain has that counts. For example, site age can weigh more that any certificate. Put the two together, then you just might have something providing you have been well behaved all these years. Simple truth.
