is 4gb enough in 2014?
For what ever it is wort, here are my personal experience.

I have a mid 2012 MBA with 4 Gig RAM and 256 Gig SSD.

It has a Mavericks OS 10.9.2, MS Office 2011, 3 Browsers ect..(browser could eat up to 700 meg of RAM)

I have 110 Gig of videos and pictures.

I am a "normal" (no offense) user thus no serious programing or heavy duty video or photos rendering. (those are the CPU and RAM killers)

So far having multiple apps open,  I have not noticed a slow down in performances.

The Activity Monitor on mavericks has a great feature called memory load, and I always stay in the green range.

I would say having more is not a must have but nice to have (so a question of Budget)