I think this is an interesting discussion and can only give my opinion. I considered the atom and the caterham and could afford either. I picked the caterham for its heritage, the usable weather gear and the funky good looks. I initially went shopping for a csr 260 because I believed more should be better, but I stumbled onto a slr with 200 hp and have found that this is plenty. I just drove it from dallas to aspen and back and used the top for some thunderstorms around amarillo and it worked well. I doubt I would have tried something like that in the atom. When I got home I cleaned it up and took off the windscreen and weather gear and its back to SLR configuration. If I had 10 cars I probably would want an atom, but I just think you can get a great driving experience in a more interesting and useful car. Now the lotus 2-11 may be a different story.
Cheers, David