Do you have to have the games on your wishlist to get the newsletters from this sale? Or are they sent only to people which have subscribed freshly with the freebies? I've not gotten any newsletter so far since the start of the sale.
A mixture of both. Some require it to be wishlisted (like the Neverwinter Nights discount from September). Others require you to own one or more games (eg Beamdog and Star Wars discounts from about a year ago). The rest simply require newsletter subscription, and quite possibly "Promotions and hot deals" checked in the subscriptions section.
In this case
Only GOG.COM's newsletter subscribers are eligible for the discounts.
So no wishlisting or purchases required.