>> Large cities have many representatives, so I don't think your proposed change would necessarily have much effect.
Look at the county map for California in the 2004 election. Assigning electors for each district, just in Cali, would have been worth about 19 or 20 EVs switched from Dem to Republican. After the 2004 election there were a lot of calls for re-working the electoral college in Cali, the pubbies missed a grand opportunity to propose something like this.
But you would lose electoral votes in Texas and Florida - some votes would go democratic. Same with Ohio, and other states too.
I'm not saying everything would even out. Applied nationwide, it might work in the Republicans' favor. And it might not. Be careful.