Justin, I am surprised you reject Marx's value theory. Tell me if any Marxist philosopher of science has made the point below.
First take Hempel's distinction between empirical generalization and theory formation. Now in the case of political economy, in the first stage we would collect data as it appears--the periodicity of the business cycle, the relation between the peak of the real wage and the onset of a downturn, evidence of concentration and centralization and their relation to growing minimum investments.
All this was know before Marx began; indeed it can be traced to William Playfair, in 1805 or so, according to Grossmann. What Marx did was move to the level of theory formation--that is he aimed at comprehensive laws, in terms of hypothetic entities--value, surplus value, rate of surplus value, organic composition of capital--that account for the uniformities established on the first level.
Hempel argues that generalisations expressing regular connections among directly observable phenomena are of the first order. Exs include even precise quantitative laws such as Galileo's or Kepler's or Hooke's.
But on the second level, we encounter in the most famous scientific theories general statements that refer to electric, magentic, and gravitational fields, to molecules, atoms, and and a variety of subatomic principles; or to ego, id, superego, libido, sublimation, fixation, and transference, or to varous not direclty observable entities invoked in recent learning theory.
Thus any empirical science has a vocabulary in two registers--observational terms and theoretical terms.
It suggests anti theoreticism on your part therefore that you want to rule out of court VALUE THEORETIC terms. It is by them that Max developed an actual scientific theory to explain the empirical generalisations (the crisis cycle, concentration and centralisation, the appropriation of the middle classes, etc) which had been noted long before him.
This is the point Grossmann wants to make in his Playfair essay. Hempel's analysis helps us to do that. At any rate, by rejecting value theoretical terms, you are denying Marxism its status as a scientific theory at Hempel's second level.
Yours, Rakesh