A3 vs L3 is probably a matter of preference. Although L3 probably has a larger market share, and a wider array of extensions as well.
No mistake though that Aperture is mostly a Pshop killer. I do an awful lot of imaging, and have not only worked with photoshop since version 1.0, I have taught it on a professional level to both designers and professional photographers. It is/was a great tool, and I have a pretty good grasp on how to use it.
If I was teaching a professional the rudimentary basics, I would probably need 3-5 days to get a professional "functional" with Pshop... I could cut that down to 3-5 hours for Aperture. The latest interation is very windows like IMO, and other than content aware scaling (which I don't think was actually developed by Adobe), there were not great leaps of improved workflow functionality. I am not going all Jobsian on Adobe, but the app is bloatware loaded with feature creep with very little huge advances despite the huge annual upgrade costs. I could name each substantial advancement if I wanted to, but trust me they are mostly incremental improvements. Despite the fact that Adobe built itself up on the backs of the Mac professional community, they have moved away to chase the larger market at large, and left us Mac folks as an afterthought. Updates are usually last for the Mac folks, and I don't feel the same degree of love that I used to have. Quark, which used to be the most hated company has turned itself around to be more warm and fuzzy company, and Adobe has kind of moved to where Quark used to be (for a lot of us at least). LOTS to quibble about there, and I don't really want to derail the discussion too far...
My point is that for many folks either A3 or LR is indeed a pshop killer, and you may be just fine with an older version like CS3 to supplement.
Case in point, a friend of mine is a professional shooter... He had a recent job that involved cleaning up around 200 images for printing for a corporate client. Previously the job took him 3-4 hours to process and correct. Using presets and the stamp settings tool, he could rip through those images in about 15 minutes. Essentially all he had to do was correct one image, and then apply the settings to the batch, and then go back and fine tune. All with just a few clicks. Way, way easier than batch actions in pshop.
I have been working in imaging for many years, and Aperture brought about pretty radical changes to my workflow. While I am proficient in pshop, I can simply accomplish things in Aperture and NIK that I could never do in pshop (at least as quickly or as easily). Yes, Apple is a bit slow with the version updates... But they are cheap, and they are substantive.
Cheers,
Michael