Just before Barney turns off the Space Teens video the first time, the math problems Alan Thicke poses is 23 times 3. The answer, of course, is 69, further fueling the joke that Space Teens is porn.
This episode is also season 6, episode 9. In other words, 6,9.
At the beginning of Let's Go to the Mall, Robin says "come on Jessica, come on Tori!" In this episode we meet Jessica, however Tori is never introduced.
Ever since Robin Sparkles was introduced, she has been pretty clearly based on Alanis Morissette. Both Robin Sparkles and Alanis are Canadian girls who started in pop music with one big hit - "Let's Go To The Mall" and "Too Hot", respectively - who after a hiatus changed to performing edgier music. The trend continues here, both were in Canadian kids' shows: Robin was in "Space Teens" while Alanis was on You Can't Do That on Television (1979). There's even a nod to this in dialogue, when listing kids' shows Marshall ends up saying "You can't do that on television", seeming to name this show but actually saying this phrase about Space Teens.