I am sorry to join this discussion late, but I was travelling and did not have the time untill now to read the material and collect my thoughts. I agree that some form of economic accrual accounting should be used for the public sector, specially for the balance sheet, but several problems should be considered.
First, accounting and the budget are tools of economic planning for individual firms, while they are instruments of fiscal accountability for the government. Other instruments of economic planning are used by the public sector, such as cost benefit analysis, social accounting matrices, input output and various forms of national and local accounts. Socialist regimes tended to confuse fiscal responsibility with economic planning with ominous results.
Second, economic aggregates are not necessarily reducible to their disaggregated components. Aggregate investment , in particular, is a form of consumption of instrumental goods (machines), industrial intermediates, raw materials and labour and contributes both to total cost and to aggregate demand in the short run, while it "may" add to production capacity in the long run. From the point of view of an individual firm, instead, investment is a commitment of resources in the hope of future benefits, so that its relevance for the construction period is only in terms of cost.
There have been various attempts at incorporating these characteristics in the government accounts. Buiter, for example , proposes to exclude investment from the estimate of deficits and debt sutainability. However, while for the firm the solution is simple : in the income statement (but not in the cash flow statement) annualize the investment according to an acceptable accounting rule, this is not so for the government, which faces the financial cash flow nature of its accounts (because of their fiscal accountability purpose). In program and project evaluation, on the other hand, discounted cash flow methods already take into account the different nature of investment as an activity of resource transfer over time.