Population trends favor Republicans

[Smash255]

Zorkpolitic, I'm sorry, but you're not really making a lot of sense here. Demographic trends based on state size is completely irrelevant. Only actual voting blocs' demographic changes are interesting. If people move around that ain't gonna change anything (at least not automatically). What could matter is if certain political groups, such as farmers or mine workers or house-wives or whatever would change in size, because these are groups with 'real' voting habits. States aren't.

Which states grows faster than the national average (and which states don't) have very significant effects on Presidential elections, since Presidents are elected by Electoral College votes from states, not by voting groups.  So if a state in 2008 votes Republican (like TX will) and in 2012 TX has 3 more electoral votes, then Republicans from 2012 to 2020 have gained a 3 EV advantage over where they were in 2008, without any shifts in voting blocs. 
I would argue that we have seen very little shift in voting patterns from 2000 to 2004, so that the addition of EVs to states Bush won will tend to favor Republicans for the next decade.  Of course candidates matter and campaigns matter, so swing states will likely change somewhat between Democrats and Republicans.  But the trend of moving EV from states Kerry and Gore won to states Bush won will be net plus for Republicans, perhaps by up to 14 EV.

That is true up to a point. My point is that unless these new voters providing these additional EVs are Republicans, which is no given, all we're seeing is a redistribution, which is not necessarily bad for the Democrats.

Exactly, especially when you take a look at where some of these people are moving from.  Some of the borderline GOP states could become tossups & tossups could become borderline Dem due to the fact that much of the growth in some of these states can be contributed to people moving away from areas such as the northeast which, and as a result of where these people move from they will tend to be more Democrats.  Areas such as Nevada, Colorado & Florida have already seen an impact like this in the past 10 years or so & thats something that could spread to some of the other growing states such as Arizona & North Carolina (though it will take awhile for any real switch in the last tewo states).

Bottom line is while the population shifts will give more EV's in the states that are currently GOP, the population shift might make these states more Democratic & more competitive as a result.