That's correct... the lounge situation is *extremely* confusing. I'm surprised you got a knowledgeable agent who explained all of that. I had one attempt to convince me that the Platinum card got access to MLL lounges... and was super surprised when I had to explain to her that they weren't the same as other lounges that Priority Pass permitted access to. Sigh.

When you mention the $50GC offer, are you referring to the GCR rebate for signing up for the Amex Gold? If so, be careful, since that loses you referral points.

YYZ-LHR is very different from YVR-YYZ because it's "international" and some companies treat that differently

As far as cards we keep, it'll depend from person to person on what their requirements are. I generally skip on most of the "non-frequent flyer miles" cards, so Scotiabank, Aventura and all that are completely out of my area of expertise. Not because they are bad, but just because they do not bring any critical value to me (I don't really care about cash, hehe). So I carry the Amex Platinum and the TD Visa, and that literally covers 100% of my daily expenses.