Hi-voltage required for 100% SoC in LA banks?
Even though your question(s) is not clear to me, I am providing the following response.  Hopefully it will be of some use to you.

From what I know, a lead acid battery is "fully charged"(100%) when it reaches 14.4V, and discharged at 12.8V.  So, at 13.6V, I would consider it only 50% charged - regardless of how long it is charged or the amperage of the charger.  If you want to "fully" charge it, you must provide it the higher (14.4V) voltage.

Obtaining the higher voltage should not be a problem, fossil fuel motors usually have a generator and regulator that provides such voltage (14.5 - 15V)!
Although it is true that "deep cycle" batteries are better able to handle deep discharges, if you expect to obtain the maximum life (cycles) out of them, just treat them the same as "regular" batteries, and they will last longer.

Now, as to the question of whether or not is "worth it" to follow the manufacturer's charge/discharge recommendations, only you can answer that.  You either have to rely on the manufacturer's specs, or perform your own "life tests."