Yep, chest freezers already use a fairly low amount of energy, and the fact that they run for maybe 5% of the time means I haven't noticed it at all on the electricity bill.
As far as wearing out the compressor... if you do things right, it shouldn't be an issue (and shouldn't be cycling on much more than usual anyways). The idea is to use thermal mass to prevent rapid temperature fluctuations. Ideally, you should tape a probe to the side of your fermentor and insulate it - that way, you are measuring the temperature of the beer, and it takes a much longer time for 5gallons of beer to change by a degree than it does for air (just look at how long it takes to boil water!). And by measuring the temperature of the beer with the thermostat, you are also CONTROLLING the temperature of the beer, which makes a heck of a lot more sense than measuring/controlling the air around it (due to the additional heat that yeast generates during fermentation.)
Temperature controllers typically allow you to set an automatic delay so that the compressor doesn't cycle on too quickly, even if the temperature settings say it should, and this gives your freezer some added protection. But it's really just a precaution, because with the thermal mass of a 5gal batch (sticking even more stuff in the freezer also helps) and proper probe placement, the length of time it should take for the thermostat to turn on the compressor should significantly exceed even the highest delay setting anyways. Basically, if you do things right, a freezer should last you a heck of a lot longer than "several years". Depending on how old it already is, it should be more like "several decades."