The processor upgrade may have value for some users who perform, in relative terms, a lot of processor intensive tasks like video encoding, or gaming. Otherwise, it is not really all that necessary. You should be fine without it.
On the other hand, the $100 upgrade for 8 GB of memory is a no brainer. Get it without a second thought. Not only is it a very reasonable price, it is something that a long term owner will value, on down the road. If you multitask, it will add zip and pep, like no other remedy can. Since you NEVER upgrade the memory, it is a good idea to get while you can. In the case of the Air, that is ony done when you order it that way.