If you're getting a Mossberg, the M590A1 with the metal trigger guard and thumb safety button is the way to go; the barrel's of a heavier thickness than on the cheaper guns, too. I think you know enough to have developed some good instincts about what you're doing, so if they telly you the mooseburger is the gun for you, go for it.
But your question was The gun show is this weekend, I've got a budget of about $500, what would you buy?
I'd buy some ammunition, and maybe a spare barrel for the Remington, product of the genius of John Browning, and go with that. Nothing wrong with the Remington Model 11 copy of Browning's Auto-5.
Over the years, some very serious users found them to be just the ticket in their line of work. Even if you get the Mossie, don't neglect the semiauto.
-archy-/-
Agree with your last post.
I bet you are familiar with the plastic safety buttons on the Mossbergs. Just about all of them will break eventually. I haven't seen one up close in about 10 years so assume they have corrected the problem by now.