The "test your API" feature sounds great! It's good to hear you're actively looking for ways to help us better understand usage scenarios.
Perhaps some information on profiling and what to expect from deployment? For example, is a call to Timing in a web development session close to what deployed code will use? Maybe a Desktop-only feature that lets you perform limited profiling deployed code from the deploying account without consuming credits? Being on the Developer plan, I'm concerned about deploying examples to show off to the world; a non-trivial Instant API call I could imagine taking 4-6 credits, which doesn't even let me handle 2000 hits.
As far as Wolfram Alpha API calls go, perhaps a small indicator in a function's documentation to show that a call is required? To use the OP's example, looking at the documentation for ElementData gives me no indication that it will count against my 1,000 monthly API call allowance when deployed. Or maybe that would be a useful item to have on the Suggestion Bar in Desktop?
Thanks for listening to our feedback!