The longevity of the SSD, and the build quality - the larger ones were better built - as much as the extra capacity were what persuaded me that the larger SSD drive was he way to go for me (that, and my large iTunes music library, which is well over 100GB - I'm not enamoured of the cloud renter model).
But, enjoy your MBA and the best of luck with it - it is still s superb computer.
A video here which supports your inclination toward the larger SSD, in a discussion of SSD longevity.
However, from my own usage point of view, I feel 128 GB should be adequate for work and occasional travel requirements. The real memory hogs, iTunes and Photos libraries, will remain the domain of my Mac Mini.