Is it worth upgrading the processor on macbook air from i5 to i7?

It really depends on your need..

If you use some heavy load programs - movie rendition/graphic etc.. i7 might be a good step up.

However, I think users chose MBA - mainly for the portability and light weight -- word processing, web surfing and simple photo editing, music/video streaming ..etc -- that i5 is more than enough.

If you have need power and portability -- MacBook Pro will be another choice. You can put all the specs together and decide which one will fit your need.