Dems generally have the popular votes from the more populous states. Their "safe states" are fewer in number, half of the votes in CA to the GOP would hurt more than gaining half the votes in Texas. I think the GOP would gain an advantage over-all, though not a major one.
One thing that both parties would probably dislike as well is, they would need to spend far more campaign dollars in states that they traditionally haven't had to.
In terms of recent presidential elections, the 11 largest states include five "red states (Texas, Florida, Ohio, North Carolina, and Georgia) and six "blue" states (California, New York, Illinois, Pennsylvania, Michigan, and New Jersey). The fact is that the big states are just about as closely divided as the rest of the country. For example, among the four largest states, the two largest Republican states (Texas and Florida) generated a total margin of 2.1 million votes for Bush, while the two largest Democratic states generated a total margin of 2.1 million votes for Kerry.
Among the 11 most populous states in 2004, the highest levels of popular support, hardly overwhelming, were found in the following seven non-battleground states:
* Texas (62% Republican),
* New York (59% Democratic),
* Georgia (58% Republican),
* North Carolina (56% Republican),
* Illinois (55% Democratic),
* California (55% Democratic), and
* New Jersey (53% Democratic).
In addition, the margins generated by the nation's largest states are hardly overwhelming in relation to the 122,000,000 votes cast nationally. Among the 11 most populous states, the highest margins were the following seven non-battleground states:
* Texas -- 1,691,267 Republican
* New York -- 1,192,436 Democratic
* Georgia -- 544,634 Republican
* North Carolina -- 426,778 Republican
* Illinois -- 513,342 Democratic
* California -- 1,023,560 Democratic
* New Jersey -- 211,826 Democratic
To put these numbers in perspective, Oklahoma (7 electoral votes) alone generated a margin of 455,000 "wasted" votes for Bush in 2004 -- larger than the margin generated by the 9th and 10th largest states, namely New Jersey and North Carolina (each with 15 electoral votes). Utah (5 electoral votes) alone generated a margin of 385,000 "wasted" votes for Bush in 2004. 8 small western states, with less than a third of Californias population, provided Bush with a bigger margin (1,283,076) than California provided Kerry (1,235,659).
With National Popular Vote, every vote would be equal. Candidates would reallocate the money they raise to no longer ignore more than 2/3rds of the states and voters.