One would think that if the framers had meant to quantify 'limited times' they'd have done it.

Then why didn't they define "unreasonable" when used with "search and seizure", or "cruel and unusual" when used with "punishment"? It seems to me they merely underestimated just how corrupt politicians would eventually become.

The point in favor of Lessig's case that I haven't seen anyone even attempt to answer is the retroactive extension of copyright on existing works. If the purpose of copyright is to assure prospective artists the chance to make back their investment, then the only benefit (to society) of copyright is its assured application to new works. In corporate terms, if we already have the deliverable, why would we want to offer any additional payments?