It'll be sad if they figure out who you and your bots are, and then deny you specifically access. Got backup plans for when you get zero results for every query because of that?
I've been involved with screen-scraping of req's for <major airplane company> to produce spreadsheets for others in the same company, and I'll take FTPing the data->CSV almost any day.
* Especially when the FAA is the eventual consumer *
We do that all the time.
Also, is zipcode the lowest level of granularity (presumably not)? Do any of these services have finer granularity?