I'm pretty sure the 12 year limit on keeping sperm is for legal reasons, not scientific ones. Organic matter gradually deteriorates at the temperatures you get in an ordinary household freezer, however the rate of deterioration at liquid nitrogen temperatures is much, much slower, and, as long as it's consistently held at that temperature, sperm would probably remain viable for centuries or longer. Perhaps the 12 year limit was put there to allow for periodic rewarmings due to technicians checking the label on the samples etc, or maybe it's just a case of legislators being excessively cautious.
I don't see anything inherently wrong with having yourself cryopreserved. Even in a worst case scenario you're not going to be any more dead than you were already, so, as long as it's not placing a burden on your still living relatives, I don't see why not. The freezing process causes extensive damage at the cellular level, so the only way you could be brought back to life is through technology far in advance of what we have now, that microscopically repairs all the damage and rebuilds you cell by cell. Who knows, that technology might arrive at some time in the future, after all, most of the stuff we have now would look like magic to people born prior to the industrial revolution. I'd agree that full body preservation is a waste of time though, since cloning a new body for you would be trivial next to rebuilding your brain.
