wouldn't it get really boring if for every mario game they just had the same basic (mushroom/flower/star) power-ups?
No, I don't think so. As long as level design is taken into consideration, all these innovations are trivial. Isn't good level design the primary reason that Super Mario Bros. is a cultural phenomenon and that Mario is the biggest name in videogames? Super Mario Bros. and Super Mario Bros. 3 set industry standards for what a good 2-D platformer should be like. Level design is what separates Super Mario World 2: Yoshi's Island, the best 2-D platformer of all time, from Yoshi's Island DS, an unplayable game.
One of the things I found so unappealing of New Super Mario Bros. was how boring it was to play it. I think if you have fun and challenging levels, it doesn't matter what retarded hat Mario is wearing, or how byzantine his power-ups are.