Of course, one big problem with a direct follow-on would have been that a year or two back the BBC Trust redefined CBBC's 'mission statement' to aim it at a younger audience: 8 to 12s, rather than 8 to 16s as before.
That left SJA a bit too 'adult' for the channel's remit, but as an existing series it was allowed to carry on as was. But if you watch the actual replacement, Wizards Vs Aliens, it's noticeably more childish (a bit too childish to be the proverbial 'Children's series that's good enough for adults). Though having said that, the last episode of season one declaring that they're not playing games any more, implying that the production team want to take it in a more serious direction next year.
I just watched Wizards vs Aliens a week ago, and it seems to me, it's maturity level is following SJA very closely. S1 of SJA was no less "childish", IMHO then WvsA S1, and the kids, I believe are older in WvsA (Seem to be 16 yr old Characters, and the star is apparently 21 in real life). And as you mention, the S1 Finale of WvsA seemed to indicate it will grow in maturity in S2, just like SJA did. I look forward to S2, even though S1 was a bit more juvenile than I would've liked
One Day I hope to be the Man my Cat thinks I am
Where are we going? And why are we in this Handbasket?