"dotations"
It appears that oyu have not looked too carefully at this method of rewarding acheivement. These grants were made from the domiane extrordinaire, the personal holdings of the Bonaparte ruling house. These holdings were acquired not from the people of conqueored territories, but from the former ruling houses. The recipients of sovereign largesse changed - from suporters and officials of the prior government to those of the new Bonpartiste government. There was no impact on the people from such a change.

Further, before we can judge if such expenditure (or any expenditure) was other than trivial in size, you will need to provide a (sourced) total and a comparison to relevant states' population, total expenses, national production or trade - so kind of scalar to measure the expenditure against. To say "examples go on and on" is not a metric, it is not sourced and it allows us to form no conclusion.
You have made an assertion of "systemactic plundering" . Merely re-asserting such without evidence is not getting us very far toward agreeing that your assertion is correct.

"N reserved large portions of the incomes of several vassal states for him to disburse as he wished."
Neat assertion. Might be true. Please state (with sources) which vassal states, how much income, and how disbursed. Comparisons to prior or later, non-Bonapartiste, practice would be nice, as you seem to imply that Napoléon did something atypical in this regard.

"But from 1810 there was no Dutch army, no Dutch navy; they were French."
Yes, of course.
Some of the Imperial expenditure for the Dutch military might have been avoided had a Dutch military policy been implemented instad of an Imperial one. But, that said, the Dutch state would have had a military of some sort, and paid for it, had there been no Empire. This (assumedly lower) level of expense should, I think, be considered a payment from the Empire to Holland.

"The taxes raised by the French imperial treasury from the old Dutch provinces presumably flowed into the imperial coffers."
Actually no. Quite unusually, they did not. Of the 60 million annual tax reciepts, 32 million were programmed for domestic expenditures in Holland and 28 million for serviceof Dutch debt. The comte Mollein is quite specific on this.

"the defence costs of such an area were liable to be high .... but it was all domestic French expenditure."
Right, and the Dutch engaged in legal business didnt pay for it. The on-going expenses were met from the Empire. The one-time expense in 1810 to re-invigorate the defenses and the trade blockade was paid from seizures of illegal goods and from the collection of arrears of customs duties on colonial goods that had been studiously evaded for many years.