A basic casino wordpress site on a random domain with a nice layout and a few articles is worth very little in my opinion. The reason is that there are nice templates out there for little money, and it also costs you little to have written a few articles / reviews.
A casino site with a standard design is only worth something if it generates traffic. Relevant traffic is what makes a site valuable.
As you have mentioned Wordpress specifiaclly: I personally think that - all else equal - a WP site is worth more than an identical site on another CMS. The reason is that there are more buyers who know how to work with Wordpress. I have bought non-WP websites in the past and I would not do that anymore - just too much of a hassle.
"Semper paratus!"
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