Note 2:
Another reason why you need a bigger mana pool is this:
https://wiki.project1999.com/Soothe costs 30 mana per cast till you get your DW arms, and you going to be using this spell alot going 30-46 ( when you get DW arms for free clicky version). Calm costs 50 mana and Pacify costs 100 mana but you rarely use Pacify as a solo Paladin since you don't really kill mob levels that are 50+ solo.
If you have a Mana pool of 1000 at 40, you're gunna run out of mana rather quick especially if you have to sooth 3 mobs to pull one out and solo it ( that's almost 10% of your mana) when you fight the mobs and you get low HP and you needed JUST that one more heal to get the mob over the line than you will curse the day you didn't aim for the biggest manapool you could get.
Note 3:
A point on mana regen side of things? yes you will have a hard time regening mana unless you get buffs and or some high end raid items/quest items, ( have they fixed the FT stack problem on this server? ) I think Paladin can get MAX FT4 stacked on p99 but it's pretty much you're life traded to attain it.
Anyone who's played a Paladin solo/duoish knows that eventually you need to med for mana, infact most of the time after you solo a mob/a few mobs you HAVE to med up. Having a larger mana pool will make your med times longer (like duh?), but you're killing at a more efficient rate/safer rate. Trust me when I tell you want that extra heal, or root, or stuns over the .25% more dps from the 20 str or the 80 hp from the 20 stm.
Note 4:
So again if you're a casual player wisdom is the best stat you can get, if you're a hardcore raider it doesn't matter what your stats are because you're just there to give the tanks a +200hp buff.