Am I correct in saying that one of the biggest issues in regards to the attendance cap is overcrowding and being understaffed? So if we wanted to find another place, ideally we'd want one just big enough that the halls aren't over crowded and people aren't getting turned away from panels, but still within the budget.
Are hotels outside of Denver out of the question? There's an Embassy Suites right off of I-25 in Loveland with a huge event center. The hotel's convention space is about the same size as the Marriot, but use of the event center for Main Events would free up a lot of that space. It might be worth looking into, if it hasn't been considered yet.