Voices add immersion, true. Heck, when the right VA does a good job on a video for a given character, its hardening efficiency is beyond questioning.
However what I felt about Najar so far is all about silent intimacy and connection with the partner, with only the physical sounds giving the ambience the scene requires. I note the subtle changes in animation, be it slight position changes or the ecstasy on a girl shifting her face expressions.
Perhaps this is just me, having ingraned into najar's style and enjoyed najar's style so much that any changes would be acutely evaluated. If you're so into audible feminine reactions that you NEED a voice to make a scene appealing, it's fine by me if fans slap a voice unto the videos and feel happy about it. Just let the default enjoyers have their silent fun, and more appreciation unto you from fellow voice fans if you find the right voices to make you happy.