There’s a petition drive is underway in Colorado to allocate the state’s electors in proportion to candidates’ popular vote. All I can find is the title as it will be presented to voters; I can’t find the actual text of the proposal (including any minumum threshold requirement or whether there will be “bonus” electors for the plurality winner), so it’s hard to judge what the impact of the plan will be.
I suspect the substantive effect of such provisions, if adopted in every state, would be minimal across the board; while candidates might arguably be more inclined to focus on the most populous states, I’m not sure that the actual benefit of such a strategy would be very large. Instead, the sensible strategy would be to focus on states where you’re close (say within 100,000 votes) to gaining an additional elector, and it’s not at all apparent that these states would be more likely to be large.
At the individual level, I suspect PR for the electoral college would somewhat increase turnout in relatively lopsided states like Massachusetts and Mississippi, and somewhat decrease it in perennial “swing states” like Florida and Ohio, but I think that would have more to do with campaign effects than any sort of utility calculus by voters.
Incidentally, there’s probably a good undergraduate or first-year graduate student paper in an analysis of the effects of various electoral college allocation systems (PR, bonus PR, congressional district, plurality), with particular focus on elections with relatively large third-party voting (1948, 1968, 1980, 1992, 1996, and 2000).