I'm going LR4 too for the underlying reasons you give plus it's just so more capable.
The lens module is great and especially useful with vignetting on FX. The adjustments, especially the astonishing "clarity" slider take you into Nik plug-in territory. The presets are better too. The native RAW conversions are far nicer
It's not at all hard to use. it's like combining Nik tools and Aperture into one thing. And I still have the Nik tolls whenever I need them. I love the Lightroom 4 unmasked e-book too.
I also never enjoyed the idea of having an Aperture database. I rather like seeing where the files are!