Assuming that the underlying propensities are, in fact, stable and given enough time-series data with sufficient variation, standard regression procedures should be able to extract reasonably robust  BIS Review 73/2001  1  estimates of any differential in spending propensities - for example, out of stock market wealth and home wealth. But, in practice, these circumstances do not prevail.
As a consequence, we at the Federal Reserve Board are in the process of developing balance-sheet disaggregations that should help us infer the propensities to spend out of capital gains across different classes of assets.