This plate was made to commemorate Glen's flight in Friendship 7 in 1962. Like most historic events, manufacturers are quick to promote and profit from this one, mass producing items from John Glen lunch boxes to ashtrays. From what we can find this plate is just another of hundreds of such pieces produced during the early 1960's regarding astronauts and space flight. The majority of these commemorative bits of memorabilia were low cost mass produced items that were never intended to to last as long as they have, or be one day be considered a rarity.
Values for them vary over time, values sometimes increasing on anniversaries of the event commemorated, then quickly dropping off again. Regardless of the demand, the ones with the highest value will be those in the best condition. As these were generally low cost, mass produced items on which the applied decoration tended to wear quickly. For this reason it's best to either display them in a cabinet or place them in storage rather than use them as tableware. In the current market we have seen comparables to this particular plate sell for at auction in the $25.00- $50.00 range.