I'm sure they have - hell soon there will be a crossover episode with Family Guy. However I think the problem with the Simpsons is they've already done most stories I think the only place they could go is actually killing off one of the 5 main family members as something they haven't done yet.
Since when? Since John K animated an opening for them once?
Oh and the crossover isn't a "risk", its another standard marketing ploy that is bound to succeed. And the problem is not strictly recycled plot, but FORCING pop culture and guest stars into the narrative simply because the writers don't know what else to do. The episodes don't feel natural and haven't been for almost a decade. Yes, the GOOD episodes of the simpsons had pop culture refences ALL the time, but it wasn't ALWAYS the focal point (occasionally they were, but at the same time the references were based AROUND a narrative rather than the narrative being based strictly AROUND the pop culture/guest stars). Because of the latter, everything feels incredibly hamfisted and artificial verses its hay day. Also they've been really…making the secondary characters extraodinarily bizzare. It is hard to note what exactly they're doing with them unless you compare them in the older seasons and their most recent depictions.