Sounds like something which will only appeal to the adults old enough to remember the original (i.e. people at least a decade older than I am), and the supposed target age group won't be interested at all. I don't think you can bring back old formats based solely on nostalgia for the original.
I don't think it sounds like that at all. Events such as the Broom Cupboard and Blue Peter anniversaries have been created with so much care and attention that they appeal to kids and adults alike.
Saturday Mash Up was sold as a continuation of the traditional Saturday morning shows and the child audience seem wildly enthusiastic about that, it certainly hasn't been overshadowed by endless references to its predecessors. I don't doubt this will be the same - besides, they're pretty much doing the same format already with Big Friday Wind-Up. All that seems to be different here is that they're adding the Crackerjack name as a bit of a nod to CBBC's heritage and a bit of interest for any parents who happen to be watching alongside them. As far as the kids are concerned, it's just a name.
There's clearly no cynicism involved in CBBC, everyone says the teams there are absolutely dedicated to kids and reach for the very highest standards.