The only time I use ten minute paladin buffs is this scenario: End of dungeon wipes on last trash or final boss. Unless the dungeon is seconds from being finished, I'd rather have the peace of mind that everyone is buffed and will remain so for the duration. If you are constantly refreshing those ten minute buffs during the run, that creates just as much downtime due to mana loss. Probably even more downtime as you are clicking group members to check buff durations, and they tend to run out during fights. Also, Glyph of Blessing of Kings, a minor glyph, reduces mana cost of the most used buff.

As far as mana recovery.............level cooking? I catch fish in Northrend and cook them up, they give both health and mana, and are very cheap since you catch them yourself. Sauteed Goby, Smoked Rockfin, Grilled Bonescale. None of those require Northrend spices, interfere with other food buffs, or have difficult to find base ingredients. Any of those foods I listed will have a tank Paladin back to full mana in the blink of an eye.