I suspect they have very little value, particularly if not bound. In my case, when I retired, I had a small truck load of bound journals (35 years X 6 different journals X 12 months). Most were bound, and I couldn't give them away. In fact, I couldn't even put them in the recycled paper dumpster because of the bindings. So, I ripped off the bindings, put them in the trash, and put the remaining paper in the recycler.
Before computers, scanning and automated indexing, old journals had some value. You could find a young student or library to take them. In the mid-60's, I paid about $200 for JACS from the late 1800's to 1960's. That was a lot of journals and they were valuable because of the early issues. In 1974, I ended up giving some of them to people who needed to fill in their series and discarded the rest.
1) Libraries will probably not be interested, unless they need select missing issues.
2) A student (like me in 1960's) might be interested, but wouldn't have much money.
3) Most back issues of the stuff I read are available on line.
Of the magazines/journals you mention, select S.A. issues may have some value. There are classic issues that a collector might want. I don't know anything abut the collectible market for Byte or Omni.
Just checked S.A. on ebay. There are a lot for sale, but not a lot of bidders. Selling on eBay could be a slow and frustrating process. This one had a bid: **broken link removed**
John