NASA really has no options
The way the budgeting process works (from Congress, the White House, Office of Management and Budget, inside accountants, outside groups) it's amazing any programs outside of defense or national security are ever passed. NASA's problem isn't a lack of foresight, it's a lack of healthy funding. Manned space missions cost ten times (at the cheap end) as much than robotic missions which causes sticker shock to all but a few people. NASA should go ask DOD for it's space funding, but there is no way any Secretary of Defense is going to tell Congress "Send my billions of dollars to NASA where they really need the money" (FYI: DOD gets just as much money if not more than NASA for space)
Propulsion wise, nuclear is impossible outside of military operations because some group in Florida will send NASA to court and NASA is unable to guarantee 100% safety.
The shuttle was only capable of going to the space station, never beyond low earth orbit. So to go further into space (like the moon as the Apollo missions) require a new vehicle. Unfortunately the Apollo specs were lost (bad record keeping) and any parts NASA has are unusable even as a template.