Not necessarily. Cache quantity is a fine balance as larger caches take longer to search through, farther back ones take longer to get data from. Go back and take a look at the old articles between the Athlon II's and the Phenom II's the addition of the L3 cache wasnt a large performance factor, and given the fairly low performance of an Atom CPU i dont think giving it more memory to work with would help, precaching is pretty good these days so CPUs tend not to need more cache memory unless they are flipping between multiple threads, when they miss it tends to be a hard miss that goes all the way back into main memory so adding L3 cache would actually increase the performance penalty of a hard miss while not actually improving performance much.
It will also significantly increase die size, and heat output, the majority of the transistors in a CPU tend to be in the cache.