Well... the principles of the formation and maintenance of the American republic are very well thought out, very well described, and to a great degree, exhibited in our history and documents.
Hardly meaningless.
...Hardly meaningless.
Your quote proclaims the meaning of "republicanism" as, basically, "the philosophy of a republican." It doesn't explain at all what that actually means, and as such is meaningless. Which, if you ask me, is the whole problem.
Republic and democracy are practically synonymous as democracy implies republic. However if we mean "republican" in the narrow sense we mean simply opposition to privet i.e. royal government. Such a position is equally meaningless because any number of different forms of government, from military dictatorship, to syndicalist anarchy, could fit the bill and be called "Republican." Quite simply, trying to determine the party platform from the name "Republican" is a useless gesture because as your def incidentally makes clear it's a vague term.