The interests of a state based on popular sovereignty are, by definition, exactly the aggregate of the interests of its people. Appointment by state legislatures rather than direct election by state citizens was done because of many of the founders distrust for democracy and desire to build layers of insulation between the immediate popular will and policy decisions, but that's orthogonal to the reason for equal apportionment rather than population-wide apportionment, which was (like many features of the original Constitution that produce unequal representation of voting citizens) largely motivated by the desire to protect the institution of slavery by increasing the relative voting power—both in the Senate and in the Electoral College which was then tied to combined Congressional representation—of the slave state.
But then, I'd also like to see legislatures appointing electors to the Electoral College …
This sounds good in theory, but the reason they passed the 17A in the first place was because of widespread corruption in the Senate.
>But then, I'd also like to see legislatures appointing electors to the Electoral College …
That's not going to fix anything either. What they need to do is replace the Constitution and adopt a Westminster parliament like every other decent democratic republic out there. How many countries have a presidential system like ours? Only a few, and they're ones like El Salvador, not exactly countries you want to emulate.