First, what Lori has done in her study (and what I did in a similar study in the Journal of Empirical Legal Studies (July 2006) and in a forthcoming article in Political Research Quarterly) is to compare the empirical evidence against the justices' own rhetorical positions regarding respect for and deference to the legislative process and to states' rights. Many of the conservative justices have taken public positions on the matter--either in their opinions or public speeches. They assert that invalidation through the exercise of judicial review should be utilized sparingly to preserve the outcome of democratic processes, and they assert the importance of federalism to our constitutional democracy. What the empirical studies show is that these justices don't always put their money where their mouths are. In fact, in our JELS article, Rorie Solberg and I demonstrate that it is the ideological or policy content of a particular law that systematically drives the justices' constitutional responses, not any "principled" position on matters related to democratic outcomes or states' prerogatives. This is a finding that holds across multiple cases. We do not dispute the fact that justifications might be available in individual cases, but our focus was on trends, not on unique dispositions.
As for the insights offered by jurisprudential analyses, there is no question that they offer an alternative perspective that can be very useful. Better to "triangulate" on a question with various methods than to use one to the complete exclusion of the other. Qualitative studies can work in tandem with quantitative ones to shed the most light on a question of interest. There is no "clash" where such approaches are viewed as complementary. Remember that we are incrementally creating a body of evidence; one study often does not and cannot tell the whole story.