Congress Poland was satellite state of Russia, not independent one. Russian troops stationed there, Russian governor was in Warsaw. That's why November uprising started.
Independent Poland (in- more or less- DoW borders) would be good ally for... Russia. Of course it'd mean leaving some lands in independent Poland, but it'd also equal to not having to deal with insurgents. Most of old Commonwealth eastern lands would of course have to stay in Russia, but Poland acting as active ally against Prussia and Austria (with potential roughly equal to Prussia- both in economic terms and population) is changing balance of power. Especially if Russia wishes to gain access to Mediterranean through Balkans, it has to deal with GB and Prussia (Austria too most likely). And Poland have some lands to regain from Prussia...