The Imajins and music sales were what made Den-O popular. The actual ratings and toy sales were no better or worse than the shows before it. Again, simply because it made lots of money for Toei doesn't mean it's such a quality product. Did any of the movies further the story or characters, or just milk the Taros for yet more cash? Again, just look at all the subpar TV shows and movies out there that are popular. I think you're letting your bias toward Den-O obscure your view of any legitimate issues the show may have.
Den-O did its job for more people than most other Heisei Rider shows. It allowed people who don't normally have fun with the concept of superheroics to do so, and it translated into money. Thus, on several fronts (especially the ones that mattered for Toei), it was hardly "subpar".
Did it have legitimate issues? Yes, all shows do. But if a set of shows has the same ratings but people are compelled to throw
more money a certain one due to sentimental attachment, then that show has won. It meant that it was able to get out from under the weight of people who just watch TV superheroes. The movies grossed the most, and even now,
people are still buying Den-O things. ...it's the Wii, man. The masses' definition of quality is far different from that of dedicated fans. It's a hard truth. This is why Just Dance is outselling Punch-Out!! The only difference is that Den-O is far more enjoyable and requires far more
thought than Just Dance.