Is the Nikkor 50mm f1.8 worth buying?

Photography is a bit of a hobby of mine. I own a nikon d3100 so I kno it won't autofocus. Is it much better the the kit lens for portraits? Opinions please

Yes, No.
Yes it is worth having IF your going to move on up the Nikon body line over the years to one there it will focus. It is a "prime" lens that tends to out perform the zoom lenses. The 50 will also work on the
full 35mm frame cameras and Nikon film cameras.So, it can be a very useful lens.

No, it does not zoom, you will have to move forward and backward to get more or less in the shot. The 1.8 is great for seeing in lower light but seldom will you want to shoot at 1.8 and with your camera the non focusing issue comes up.

I for one do not own a 50mm. Macro 55mm, yes and it is only used for close focus and copy work.

Take a look at where your zoom is used most often. If it is right around the 50mm area say, 40-60
then a sharper, smaller easy to see with 50 1.8 would be a good deal.

If you "know it all" why are you asking questions? For portrait work, why would you want auto anything. You should set your own focus, lighting and exposure/time.