I don't think E+ purchase would count as it's not technically part of the fare.

What might work is buy your cheap economy fare bucket and call to upfare one bucket (e.g. buy S, call in and upfare to W). But even as someone who likes arguing, I would not love to have to argue with the insurer about whether that counts. No reports on this thread that I'm aware of.

The whole point of this kind of insurance is peace of mind, so if you are unsure whether something will count, that doesn't really provide you with peace of mind.

Actually, now that I think about it, Trip Cancellation insurance doesn't even require a common carrier. If you pay for HI hotel with the CSR, and you have to cancel for a covered reason, the hotel should be reimbursed regardless of whether you bought plane tickets or arrived by private sailboat. And since airline tickets don't have change fees these days, you could just keep those as future flight credit to use within the next year and not worry about insurance with that expense.