The Space:1999 merchandising explosion was a one year affair but some really cool toys made it out during that period. The pinnacle (for me, besides the Mego figures) is the Mattel Eagle Playset with figures, this was two years before Star Wars, nobody had ever done a space ship with 3 3/4" figures before.
I've owned this piece several times in my life, it's HUGE and doesn't really fit in with my collection, I always end up selling it and losing money. I saw one last month at a toyshow and came close to a "re buy" until i had a premonition of what my wife would say. Common sense sometimes doesn't apply in toy collecting.