I guess I'll go against the majority here. I'm not far from you at all and currently have 12 games in my garage. The walls are insulated, as is the garage door. Does it get hot in there in the summer? Absolutely. Have I ever seen any cosmetic, electrical, or mechanical issues due to this? Nope.
My previous house in Dublin, CA also had a similar number of games, insulated walls, and a non-insulated door that faced afternoon sun. It got even hotter in there, but again, no issues.
A bit more anecdotal feedback is that my Dad also lives within a few miles of me and has had 20+ machines in his garage for over 20 years. Again, no issues.
The *ONLY* time that I have seen issues is when we had three games stored in the house. Those three games unknowingly got their cabinet art sun bleached from being too close to a window. I suppose that could be a concern in your case if the games went in the living room.
To be fair, if my collection included EMs with their fragile backglass artwork, I would unquestionably be more paranoid. Most of the games in my garage are system 11 and later, though, and almost all of them use a translite for the backglass, which seems to have shown itself to be very dimensionaly stable over the decades.
PS. You can probably fit more games in a garage without your wife caring than you can inside of the house