If they have that much propellant left at 2012, then it seems to me they're flying Cassini way too conservatively. Cassini was built to examine Saturn and its moons. The instruments were optimized for that environment. We spent billions on Cassini. Odds are we won't be sending another major probe to Saturn for a long, long time. We need to make the most of this opportunity. IMO, they should burn the propellant necessary to visit all of Saturns major and most of the minor moons. Once that's completed, boost it to an orbit high enough to avoid contaimination.