Okay, I'm liking your thinking on the Maserati as I'm quote prone to buying things just because I want to myself.
I also hadn't realised that Overfinch seem to have gone from a high performance tuning company to a business that adds extra bling to the most blingy cars currently available out of the box, so sorry for posting that link.
I know you're looking for a 500+bhp convertible with four seats, but that's a big ask due to the structural rigidity of a convertible not being as inherent as it is in an enclosed shell, so there really aren't going to be many production cars that fit that brief.
Depending on your budget, you could commission a Stateside Hot Rod & Custom Garage to build you a big four seat American cruiser with Auto transmission, A/C, cruise control and a 500hp V8, then have it shipped over here. That would definitely get you some positive attention, just be careful in the corners.
Alternatively, our American cousins offer some pretty impressive high performance coupes these days, and if you really want the mostest power in a production car, then take a look at the Dodge Demon -
As standard it was a single seater, but you could tick the options list for a front passenger seat, rear seats and a carpeted trunk for the eye watering price of an extra $3. Yes, that really is three bucks for three more seats and a carpet.
Good luck with your quest for awesome power!