Writing this review of Justice Breyer’s book, Active Liberty, in the Harvard Law Review, Judge Michael McConnell opines (p. 25 of the pdf):

Perhaps Justice Breyer means only that courts should be more attentive to empirical evidence of consequences, as opposed to focusing on abstract intentions. But again, his campaign finance example raises questions. Justice Breyer’s account of the likely consequences of the campaign finance statute consists essentially of an uncritical recitation of the stated goals of the statute. The campaign laws “seek” to further a “democratic objective”; they “seek” to “democratize the influence that money can bring to bear upon the electoral process” (p. 47). Strikingly, he does not discuss the consequences predicted by the statute’s opponents, such as the entrenchment of incumbents by making it more difficult for challengers to raise sufficient funds to overcome the advantages of incumbency, or the redirection of contributions to shadowy independent groups that would be less accountable to public opinion than are political parties and official campaigns. He explicitly defers to Congress’s judgment on the ground that “the extent of the campaign finance problem” is a matter “about which the legislature is comparatively expert” (p. 49), without noting that it is also a matter about which incumbent legislators have a rather obvious conflict of interest.

At least in his concurrence in Shrink Missoui, Justice Breyer does note the incumbency protection problem. Shrink Missouri, 528 U.S. at 403-04 (Breyer, J., concurring) (“We should defer to [the legislature’s] political judgment that unlimited spending threatens the integrity of the electoral process. But we should not defer in respect to whether its solution . . . significantly increases the reputation-related or media-related advantages of incumbency and thereby insulates legislators from effective electoral challenge.”)
As I noted in a 2004 article, “Justice Breyer, in setting forth his participatory self-government rationale, has noted the Court’s important role both in balancing competing constitutional interests and in ‘evaluating the risk that reform legislation will defeat the very objective of participatory self-government itself; for example, where laws would set limits so low that by elevating the reputation-related or media-related advantages of incumbency to the point where they would insulate incumbents from effective challenge.’ The Court, however, has failed to meaningfully balance or closely examine new campaign finance laws for self-dealing.” (footnote omitted)