I've been upgraded to a suite without using a SUA at the GH. Like any other hotel, it depends on occupancy. It's not true that they "rarely" give them out. They follow the rules and give them out if they are available. I'm not sure what occupancy is like right now. It was crazy the last 2 times I've been; I'm not sure if it's settled down a bit.

As OP asked about a "decent" upgrade, I find that the deluxe room at the GH is sufficient, which is a common upgrade from the standard room. The rooms are large. But yeah if being in a suite is important to you then use the SUA (this is true at any property)

Breakfast is at the lounge only. If you are paying cash you can always book the Privé rate which will get you restaurant breakfast, a one-category upgrade at booking (not guaranteed, but you will know immediately), some credit to use at the hotel, and an amenity of some sort, in exchange for paying the standard rate. Depending on the difference between the standard rate and the member rate, and the length of your stay, the hotel credit might make this a wash. I do this sometimes at hotels where I don't want the lounge breakfast, but at GH I prefer the lounge breakfast.