In the Washington Post, Alexander Heffner suggests that John Adams should be honored with a monument on the Mall.

What's the case for Adams? Before the revolution, he was the nation's first attendant to the American legal tradition of due process, defending British soldiers who fired on colonists during the Boston Massacre. One of Massachusetts's representatives to the First and Second Continental Congresses, Adams was a champion of separation from England and the fiercest advocate of Jefferson's declaration. Without his persuasive speeches in the Philadelphia chamber, the document wouldn't have been signed. While Jefferson was silent during what he considered the convention's editorial debasement of his work, Adams defended every clause, including an excised call for the abolition of slavery. Jefferson called Adams "a colossus on the floor" of the Congress. . . .

Heffner goes on to note Adams' services in the American diplomatic corps during the revolution and his Presidency (noting the lamentable Sedition Act as a rare mistake).  I'm not sure I'd put it quite that way.  I would, however, stress Adams' constitutionalism.

As the principal author of the Massachusetts Constitution, and in other writings, Adams, more than any other single figure, is responsibe for the U.S. having a constitution featuring an executive with a qualified veto, a bicameral legislature, and separations among the legsilative, executive, and judicial branches (separations which were not full and complete, so that each branch had to defend its turf against the others).  By paying tribuite to the author of the Massachusetts Constitution, we also, by implication, pay tribute to the people of Massachustts who are responsible for the idea that constitutions should be created by special conventions and ratified by the people.  Not coincidentally, the Massachusetts Constitution has the best concise explanation of the reasoning behind that process of any document of the era:

The end of the institution, maintenance and administration of government, is to secure the existence of the body-politic; to protect it; and to furnish the individuals who compose it, with the power of enjoying, in safety and tranquility, their natural rights, and the blessings of life: And whenever these great objects are not obtained, the people have a right to alter the government, and to take measures necessary for their safety, prosperity and happiness.

The body-politic is formed by a voluntary association of individuals: It is a social compact, by which the whole people covenants with each citizen, and each citizen with the whole people, that all shall be governed by certain laws for the common good. It is the duty of the people, therefore, in framing a Constitution of Government, to provide for an equitable mode of making laws, as well as for an impartial interpretation, and a faithful execution of them; that every man may, at all times, find his security in them. 

I am not sure, however, that a neo-pagan temple in Washington would be the bests tribute to Adams.  John Adams is more than a founder of the American republic, he is also the patriarch of one of the most extraordinary families in American politics and letters. Adams also dwelled upon the importance of education.  He put a strange clause in the Massachusetts constitution on the subject:

Wisdom, and knowledge, as well as virtue, diffused generally among the body of the people, being necessary for the preservation of their rights and liberties; and as these depend on spreading the opportunities and advantages of education in the various parts of the country, and among the different orders of the people, it shall be the duty of legislators and magistrates, in all future periods of this Commonwealth, to cherish the interests of literature and the sciences, and all seminaries of them; especially the university at Cambridge, public schools, and grammar schools in the towns; to encourage private societies and public institutions, rewards and immunities, for the promotion of agriculture, arts, sciences, commerce, trades, manufactures, and a natural history of the country; to countenance and inculcate the principles of humanity and general benevolence, public and private charity, industry and frugality, honesty and punctuality in their dealings; sincerity, good humour, and all social affections, and generous sentiments among the people.

That being Adams' view, I would say that the most fitting tribute to Adams would be to create an Adams library of American letters, dedicated to the study of American politics, with politics and literature both understood in the classic fashion.  Such an institution, which I am not the first to recommend, would be a proper legacy for John Adams and his extraordinary family. What better tribute, and what better form of civic worship, than study.  As Adams put it in the Massachusetts Constitution:

A frequent recurrence to the fundamental principles of the constitution, and a constant adherence to those of piety, justice, moderation, temperance, industry, and frugality, are absolutely necessary to preserve the advantages of liberty, and to maintain a free government: The people ought, consequently, to have a particular attention to all those principles, in the choice of their officers and representatives: And they have a right to require of their law-givers and magistrates, an exact and constant observance of them, in the formation and execution of the laws necessary for the good administration of the Commonwealth.

A library, dedicated to the study of those principles, and their continuing relevance to our politics, would be the best way to honor this founding father.