It would possibly be worth your while Googling Photoshop CS6 3D and working through a few of the video tutoials.  A few days ago they were thin on the ground, but there seem to be more every day.  There is a scattering of the better ones in this flickr group thread.  http://www.flickr.com/groups/photoshopsupport/discuss/7215762973802432 4/

I'm not sure the question is being asked specifically enough, to be honest.

I've little experience with 3D myself, but I can see a definite efficiency advantage to just editing extruded text, for example, then re-rendering in Photoshop.

With what little experimentation I've done, having the ability to make changes, for example to lighting angles, then seeing the result right away against the background photo allows one to iterate more quickly, and that seems likely to mean you'll be through with something that looks quite realistic more quickly.

But I don't know whether you're working with 3D objects added to existing photos, or full scene rendering soup to nuts in 3D.

-Noel

I've struggled with this kind of question a while to decide if worth extra $$$ to get CS6 extended vs. std.

After trial use it is very clear to me...CS6 extended not worth more cost to me. Why? because the 3D tools offer nothing compared to all the other 3D programs I already have and use. Workflow actually easier as I already know my 3D tools and they can be active as same time as Ps so moving files between apps is easy.

OTOH, I can see that if someone only dabbled in 3D and did not have other 3D programs (even some that are free), then 3D in Ps would be valuable. And there are other "extended" capabilities for scientific work.

So in the end it is a personal decision based on what kind of work you do and what tools are needed and work well for you.

One thing you could consider is to download the trial version, which provides all the features of Photoshop CS6 Extended, and actually try it out for a month.  Try actually doing the kinds of work you're anticipating doing.  You'll get familiar with the tool's capabilities, and you can not only judge the ease of use for your application but also the results quality.

-Noel

If you only plan to do basic stuff then Ps may be a good solution but it is expensive compared to free Blender.

But Ps is easier to use and Blender has a steep learning curve.

There are other easier free/low cost simple 3D programs that may be sufficient compared to the premium price of Ps but none are well integrated with Ps; but using layers in Ps with rendered 3D scenes in 2D is easy. 

Importing 3D objects from other 3D programs to Ps has occasional issues but only needed for complex work when Ps can't create internally. But if you have Ps-extd, then need for other 3D is only when more complex 3D is used.