In Jeffrey Anderson's post arguing against Pennsylvania's plan to switch from a winner-take-all system and award its electoral votes by congressional district, like Maine and Nebraska do, he writes that the plan would "render Pennsylvania essentially irrelevant in the presidential election." Jonathan Bernstein writes the plan would make Pennsylvania as relevant as Rhode Island.
There may be good reasons to oppose the plan, but that's an overstatement. If Pennsylvania were to allocate its votes by congressional district, there would still be a number of competitive districts in the state. In the 2008 presidential election, both PA-3 and PA-12 broke 49%-49%. Both PA-16 and PA-17 broke 51% for McCain to 48% for Obama. PA-15 went for Obama by double digits in 2008 but was 50%-50% for Bush/Kerry in 2004. There are a few other districts that went big for Obama in '08 but came within a few points in 2004. The winner of the statewide popular vote would also get the two electoral votes that aren't tied to congressional districts. So with five to ten electoral votes up for grabs, candidates would spend at least as much time and effort during the general election on those districts as they would the state of Iowa, which has six electoral votes, or as much as they do in Colorado, which has nine electoral votes.
Again, Anderson outlines some reasons to oppose the plan. While it may help Republicans in the short-term, it could have unintended consequences. I don't see anything inherently terribly unfair about winning 55% of the popular vote and racking up 52% of the electoral votes. But it's possible that Democrats would respond by re-doubling their efforts to institute the National Popular Vote, which would truly be a constitutional nightmare. As Anderson writes, "Imagine if every vote had to be recounted by hand nationwide — because the popular vote was nearly tied — rather than merely in a few counties in, say, Florida."
As a constitutional matter, Pennsylvania can award its electoral votes however it wants: "Each State shall appoint, in such Manner as the Legislature thereof may direct, a Number of Electors, equal to the whole Number of Senators and Representatives to which the State may be entitled in the Congress...."