Anthony,
What I have noticed is an improvement in capacity when they are given a good work out occasionally.
I first noticed this when I decided to do a capacity test on One of my 8 banks. After the test and recharge I noticed all of these batteries had somewhat better specific gravity readings.
For the whole bank generally I have had time when relos have stayed with a young baby and run a oil colum heater o/n so total days consumption was around 20Kw.
Obviously this has to be replaced but overall battery voltage o/n (without this load) is higher.
Also I now run a coolroom off Re in summer with similar consumption and the batteries love it.
Battery chemistry is complex, and full of compromises, with a few hard and fast rules.
Lead acid batteries can sulfate up if left static for months. That said I have some batteries that were "spares" that is charged and placed to one side with no further action and they are just fine.
In my opinion provided you use yours every so often, say monthly they should be OK. Oh and there is no substitute for a high quality hydrometer, specific gravity comparison between like batteries is a good indicator.
Its a big subject with a lot of miss-understanding, with much personal preferences, but enough for now.
allan down under