the New Releases topic might be one of the biggest sources of traffic for a lot of games where the developer did no other marketing
I'm...not sure where you'd be getting this idea from? My experience is that I tend to pull a decent number of upvotes, enough not to immediately sink to the bottom, and that gets me maybe 3 or 4 click-throughs from my Release Announcements link. Fewer click-throughs than people who bothered to upvote it.
Posting there is harmless and you might as well do it, but I think you're massively overestimating how much of a difference it makes, and without upvotes I'd expect fewer people to even bother to check the forum in the first place. Besides, people would sink pretty quickly there either way--it looks like there's been 4 new release announcements right now in the past hour alone.
If you want the benefits of marketing, you have to do marketing, unfortunately.