Why only 1pt in Smite?
All paladins that use holy shield have at least one point in smite as prerequisite.
Smite damage roughly depends on active damage auras (might,concentration,fanaticism), skill points invested and totally skill level of smite and holy shield,( since smite has no synergy), type of shield used (every shield has a certain base smite damage), enhanced damage % from the gear (eg. ed%jewels,fortitude etc) EXCEPT from the main weapon itself, total strength of char and last but not least +damage modifier from weapon.
The skill qualities of smite (ignores ubers' defense, uninterruptible, stun/knockback etc) are the same whether we talk about 1 or maxed. Same goes for crushing blow and open wounds effect.
As we can see the only actual difference between a build that has only 1pt in smite and one that has maxed it ,is only this, the level of smite itself. At this point we can guess that a maxed smite build will naturally have bigger smite damage in the end, with the same gear used, but we don't know the exact difference.
Test gear. I'll try to keep it as simple as possible.
Char with lvl 20 fanaticism,20 lvl holy shield,1pt smite.
Gear. Zakarum shield, shael phase blade (max smite speed, doesn't really matter but just asuming), fortitude armor, 150 strength.
His total damage is 966-994.
The same exactly char/gear with maxed smite this time will be dealing 1259-1296 smite damage.
If the zakarum shield is an upgraded herald of zakarum and the weapon is now a double shael heaven's light 3+ skills the damage will be like this.
1pt smite=1392-1424
20pt=1765-1806
A bit less than 400 average damage per hit. In my book this difference may be significant for pvp but insignificant for ubers. The chars have the same amount of crushing blow so they will reach at the last sliver of uber life simoultaneously and the maxed smiter will probably just be few seconds faster.