So I would say it's more than "barely" but not up to "substantially". Having said that, I'm totally pleased with the utilization of my MBA 13". The majority of time it does function as my downstairs desktop, but when I do travel for business, it's unbeatable. I've used it more than my company-issued dell clunker. If I need files on that boat, I simply email them to my iCloud account and use as needed.
If I didn't carry it with me on travel, and, as you, it stayed on the desk, I'd go for the MBP, with least ram and HD, then upgrade that sucker's ram and go to OWC's 480 GB SSD. I LOVE the speed of the SSD. If I'm disappointed in the 2012 MBA, I'm immediately replacing my 256GB Apple SSD with the OWC 480GB module. With that, I don't really see a need to upgrade for the next 3 years.