I hope you know I agree with you,
I am puzzled though that if they were such strict grammarians,
why they chose to follow a semi colon with an uppercase letter.
Perhaps the reason is as simple as it ‘looked’ better on the written page...
A good discussion could also be had about the meaning and intent of last phrase regarding the “other powers”.
Not only upper case after the semicolons, but in words peppered throughout in the middle of sentences as well, both in the Constitution and the Declaration.
The last clause in Article I, Section 8 corrected a document wide defect in the Articles of Confederation.
For instance, under the Articles (Section VIII), the states were to provide funds for the “common defense and general welfare” (sound familiar?) in proportion to the value of each state's real estate. The problem was that Congress had no power to compel the states to provide the funds. Why grant authority without the power to implement it? The states knew this and regularly gaffed off their duty and responsibility.
The “make all laws necessary” clause corrected this crippling error in the Articles.
Any noun could be capitalized under the rules of proper English grammar for the time.