At last, something I can respond to with authority. I just switched from Strata to Carrara at the end of December.  Strata was my first 3D program and my primary work-horse for the last 9 years.

You are correct that Strata's renderer is tough to beat. Strata can create beautiful shadows, reflections and transparency, but it takes a long... looonngggg time to render. Which means it is limited to stills for the most part.  It has some rudimentary animation capabilities, but with no function curve editor and a recently rebuilt, but still quirky, bones system it's not much of an animation package beyond simple camera fly-throughs.

They also recently added subdiv surface modeling so that may be equal to Cararra--I haven't used either much since before Strata added the subdiv modeler anything complex you wanted to build in it had to be "skinned" (called lofting in other 3D programs) which was very limiting so I purchased Silo as my main modeler.

One of the biggest differences I've found (unexpectedly) is the flexibility of Carrara's shaders (texture room).  Strata focuses primarily on image based texture maps. The few shaders they have are pre-programmed and only modifiable by predefined settings within the shader's interface.  In other words you can't mix and match shader attributes like noise or turbulence on a per channel basis but only as an overall texture to be applied to your object as a whole.

Then there is the small matter of price.  Base price puts Carrara at half the cost of Strata.  But more importantly the last update to Strata only added the ability to interact with Photoshop (like Daz does with 3D Bridge) for a cost of $150.  That was about the same price that Carrara was on sale for this December.  So I could pay for yet another "upgrade" to Strata like I have paid for over and over again for marginal improvements OR I could pay the same amount for another 3D package with a lot more features.

By the way, the image you chose is by "Nathan Koga" he does some incredible stuff with Strata but it's hard to tell how much of his images are made in post production.  I've asked him myself, but never got an answer.  Just keep in mind people like him tend to get results like that from whatever 3D program they are using--they keep at it until it looks the way the want it to--Software be damned.

For a feature comparison, outside of rendering (raydiosity) I can't thing of any features Strata has that Carrara doesn't.  But Carrara has: physics, morph targets, f-curves, channel based shaders, terrain generator, surface replication, tree generator, realistic sky and clouds, sub-surface light scattering, translucency, interactive hair/fur, and a lot more I can't think of or haven't discovered yet that Strata is missing.  There is a positive side to not having all those features too.  Strata's interface is really clean and easy to work with.

So I hope all that helps, in the end if you can afford $700 for a great stills renderer Strata might be worth it.  Lord know I keep using it for that purpose and probably will be for a while yet. But if you're into animation or do a lot of outdoor and terrain renderings you're going to find Strata pretty useless.

You can check out my Strata gallery here if you like:
http://www.stratacafe.com/member.asp?ID=6592