There are two elements provided to Google here: service viability and the purchasing data from the testing period.
It's certainly open to debate, but I'm questioning that the delivery itself is compensation enough for everything that Google is receiving from the testers. Obviously Google (and you) thinks this, but I don't agree that there's only one possible value-based assessment of the relationship.
Whether or not free same-day delivery is fair compensation for your participation is a relevant topic.
But your characterization of it I found disingenuous: "Am I to think of Google as just another buddy who needs a lift to the bus station?"
There's no reason for the snark, and to pretend like Google is just trying to score a freebie like your hypothetical mooching friend is framing the argument disingenuously. The cost of delivering something same-day is non-trivial - Google is not expecting a freebie, though you are of course welcome to value your privacy above that dollar amount.
I don't think that it's unreasonable to say that Google gets the purchasing data for free in this deal, but these things are quantifiable, right? The value of the shipping and the value of the data? The data might be harder to arrive at a number, though, since purchasing data can be reused over and over for different metrics, increasing its value.
I'm not sure what, "you're not all that" means, but as mentioned elsewhere, Webvan and Kozmo provided the same product and, I'm guessing, value...for naught.
