How to justify the expense of Photoshop

You ask how to justify the expense of PS.  If you will make any money from your photographs then the expense can be written off against sales.  Do you plan to do graphic or web design?

For me the largest expense in CS6 is the investment of time required to achieve fluency with that suite of programs. I've started down that road several times. For the photography enthusiast with anything less than the professional standard equipment the expense of buying and learning CS6 seems utterly superfluous, unless you were to undertake learning it for the formidable challenge that it would be. In which case, dive in!

Topaz plugins work just fine with PSE10 and I assume PSE11.  Additionally the Elements products now offer full layer functionality.  Also, the difference between 8bit and 16bit images doesn't seem meaningful if your workflow begins with the LR develop module. As I understand it, the finished exported jpegs are all 8bit files.

In my experience and for what I hope to achieve, LR4.2 and PSE10 with plugins are the perfect combination. They offer more functionality than most non-professionals will ever use at a small fraction of the cost.