Will a $500 bluetooth speaker give home theater sound?

Only if it says BOSE on the front

Highly doubtful, but still possibly a minor upgrade on the microscopic speakers shoe-horned into most skinny LCD televisions these days.

You can get a full blown home theater soundbar for a fraction of that....  I was looking at a new £50 ($69) 40-watt thing from Sharp (doesn't have new fangled things like Dolby Atmos)... but instead taken a gamble on an 9yr old Samsung 120-watt thing on Ebay for £55 ($76) instead, similar to what was around when I bought my HDTV in the first place.

If you hunt around you can find all sorts of perfectly good home theater kit from the likes of Panasonic / Yamaha / Denon / Sony, etc by people making space for newer stuff (or the wife / girlfriend kicked up a fuss and made them downgrade to something simpler when they moved in together)

As home theater sound demands five speakers as a minimum, with sound coming from more than one direction, of course not.

No, it will not. 

Home theater sound can be had only from equipment made to deliver it.