Now they're $400 each and I'm thinking I've been lucky without the flooding issue..so..I'm trying to decide if being pro-active is the way to go..
Everybody wants to be proactive until they bust their knuckles. Or break something on a Friday night.
I know water heaters get a bad rap past the 10-year point, but some of that is the fault of the owners who pay no attention to maintenance. Of course it's also tough to do that type of maintenance when a tenant is standing nearby wondering when you'll be done.
The other poster's advice is good-- have the water heater in a drip pan with a drain. If you want to learn about the leak as soon as it starts then spend extra for the leak detector. Otherwise hope that everything flows downhill out of the house.
I've read plumber's recommendations that when buying a water heater you should first replace the plastic-body drain valve with a brass one that has a real metal handle. The idea is that you'll be more likely to use it every month or two to flush a couple gallons out of the bottom of the heater to move out the sediment. If that plastic valve breaks while the water heater's installed then it's a real PITA to fix.
Another recommendation I've read is to pull the anode rod before you even install the water heater, and reinstall it with Teflon tape on the threads. That makes for easier removal a few years down the road. This is somewhat of a challenge because an empty water heater doesn't have the mass to help you wrestle with a tight anode rod, and a full water heater is a lot easier to apply the torque to. But however you do it, once the anode rod is easier to remove then you're more likely to check it every 2-5 years.
A third idea is to use a whole-house ion-exchange resin-tank water conditioner. They're more expensive than a water heater but they practically eliminate calcium, magnesium, and other mineral deposits in your plumbing (and in your water heater). They're a $500 investment, another $250 if you pay for installation, and a $5 40-pound bag of monthly salt. However their reduced deposits are priceless for using less detergents, cleaning toilets less often, and tripling the life of your water heater.
Our rental's water heater is only 14 years old. We wait until we're between tenants (or until they're on vacation) to check the water heater's anode rod. We flush it every few months when we're over there for maintenance. Our rental home is plumbed for gas so we'll buy a high-efficiency heater in another 10 years or so.
Burned-out elements are cheap & easy to replace. The trick is to remember to refill the water heater all the way up before you turn the electricity back on to the heater element. Oops.
Our home's water heater is solar. We bought it used in 2005 when we replaced our electric water heater, and it's 10 years old. It has some annoying "idiosyncracies" in its design, its pump, and its backup electric heater-- so I'm ready to replace it with a new solar model whenever we get around to finding one we like at a home show. They also seem much more efficient than even 10 years ago.