There is a reason why developers such as Treasure are one of the most successful developers in the industry; in Treasure's case, their reason behind their success is because they refrain from making a sequel to a game (which might explain why we'll never see a Mischief Makers 2 in the future) and they want every new game they make a totally new experience. However, that did not stop them from making this game.
And that much proves that the whole thing of "Treasure hates sequels" is a myth.
The truth is, as the President of Treasure himself once put it, is that it's difficult to make sequels to games when either one of two things is in play:
1) Licensing/contract restrictions
2) Available personnel
The first thing is a natch thing; Treasure can't make sequels to games when they don't have license any more. That's why it took them about almost a decade later to come back to the likes of Gunstar Heroes and S&P; they didn't have the rights. Sega and Ninty, as the respective publishers of both games, retains the rights. You wanna see more, then hope Treasure makes a new contract deal with those parties. Same thing with Yuke Yuke Troublemakes (Mischief Makers). Enix holds the rights.
The other thing is the personnel themselves. The pres of Treasure said that he really would only want to see a sequel to any of their games made, when as much, if not all, of those originally involved can be on call once again. Considering how many of the peeps at Treasure could finish one project, and then immediately split off and join other teams within the company for other projects, that's yet another thing.
Even Hideki Kamiya (DMC, VJ, Bayonetta, Okami), another one thought to "hate sequels", has gone on to say he definitely does NOT think that way.
For example, he would have loved to have made DMC2. But as soon as the first game was finished, Capcom had already started ANOTHER team to make the sequel. And as soon as some one else touched "his chick", he has no interest any more. This same thing was repeated recently with Okami...he was all for the idea of making a sequel, until Capcom unveiled that DS knock-off. Viewtiful Joe and Bayonetta are all he has at the moment. I hope Capcom or Sega don't screw up things any...