SWs have ALWAYS, since Oblivion, been used as an exciting marketing ploy. As soon as it was reused away from the SW1/SW2/Nemesis project, it became the stock codename for all large coasters. That's all it is.
Rita wasn't because it didn't 'qualify'. It was just a coaster, it was unthemed, and didn't bring any major change to the park. DIC-Tussauds had no interest in building SWs, so Rita was just a coaster. Same for Sonic.
The Secret Weapon codename, in my opinion, is a tired and outdated concept.
The reality is that it was dead after they built Oblivion. It worked for Nemesis and Oblivion, and to an extent Air, but after that I feel the SW "series" came to its natural conclusion.
The idea of the "secret weapon" showed to be nothing more than a fat gimmick with Th13teen. Heck, even more so than the world's first element itself. Remember that tacky bit of PR they did when the "element" was delivered on lorry with SECRET WEAPON plastered over it? Exactly my point.
If you think about it, if Th13teen had not been given the label, we would not have expected so much from the finished product. Even if they had still marketed it as the best thing since sliced bread, like they did, without the SW status we would have just accepted it for what it was, a family coaster. The Secret Weapon status places too high an expectation on new attractions which they are no longer capable of producing.
It only ever truly worked for Oblivion. Why? Because it was actually meant to be a "secret weapon" given its theme which the ride originally planned for the Nemesis site was going to have. With Nemesis, I don't think anyone outside of the top management even knew it was codenamed SW3. It was just an internal thing relating to the plans.