Using whenever in OP's examples always strongly implies that the "conditional / hypothetical" scenario referred to has happened more than once in the past (and could be expected to happen again in the future).
You can use plain when in the above context, but this version could also be used to refer to some expected future situation that's never happened before.
Using real-world pragmatics (which actual situations are more likely?) it would be easy to simply say that only when works with the "millionaire" example. But obviously there are at least some people (Donald Trump comes to mind) who have become millionaires more than once in their lives.
Note that to some extent, using a future tense after when implies the "hasn't happened before" context, so given the alternatives...
1: When I get money, I spend it instantly
2: When I get money, I will spend it instantly
...we naturally tend to interpret #1 as having the whenever sense (past and future), and #2 as referring to a single anticipated future event. But be aware that sometimes, perfectly competent native speakers will use #2 even if they intend the whenever sense (it's really just a relatively uncommon stylistic choice).