Ray, a polished surface is simply one where the scratches and surface imperfections are smaller than the wavelength of visible light. That is, it's still "rough", but you can't see it.
P1200 paper has a nominal grit size of 15.4 micro meters (I didn't know that - I've just looked it up!) and light has a wavelength around 0.53 micro meters. Old, used 1200, used wet, will get you near to that wavelength, but you'll need something finer to "polish" it.
T-cut contains very fine particles of grit and scratches off a very thin layer of paint when used on cars, and will similarly remove a thin layer of resin when used on your hull, and it should "polish" it ok - but do try going down the sandpaper grades first: it might make your job easier if you can get a finer paper than 1200.
Andy