Well here's my reasonings and thoughts.
Topping off a system once a day will harm nothing. Before ATOs were utilized, this was simply "the way". I have actually in the past been lazy and skipped a couple of days without topping off with no harm. Salinity increases, as long as they are done slowly, will not harm anything and sudden decreases in salinity are harmless as well. The salinity of the reef is very volatile, almost as volatile as the temp and routinely goes through large slow swings. It's not rock solid stable as we are meant to believe as aquarists.
Lime water is a very safe method, this is the majority of the reason why it is used. Generally, corals and fish are not effected by pH to a certain degree. People have kept successful reef tanks at a incredibly wide range of pHs. It's alkalinity swings that harms them. The only reason that pH will affect anything is because of what it does to alkalinity, not the pH itself. Saturated Kalk actually doesn't have a whole heck of a lot of alkalinity and overdoses of Kalk are much much much safer than an overdose of two part. Most of the time a Kalk overdose doesn't even require any kind of intervention.
http://www.reefkeeping.com/issues/2005-07/rhf/index.php#11
As for wear and tear, while 20 beans isn't a big deal. It's still 20 beans. Penny pinchers like myself don't want to spend that money if it is avoidable. Plus it will be the one time that your gone on vaca that the ATO pump fails, and the tank evaporates over the course of a week or two and you come home to a burned up return pump and other disasters because it's been running dry for a week solid. I forgot to add that it's a good idea to plumb multiple pumps into the same ATO powered by the same float switch just in case one of them decides to die.
:beer: