The raise in power isn't as good as doing it for cost.
at high lvls a SS can recharge them selfs and recharge others.
Have you compared actual ingame experience from this? I'm not sure if my calculations are 100% accurate but from the table it would seem that power yields better results than cost. Do you know of any recharger that went the + power route?
The only thing about that chart that is flawed is the "in-between" time. A recharger, will not (and probably cannot, unless having Seraphim buffs) recharge constantly for the entire length it takes to empty the mana pool. There is the regen time, inbetween recharges. However, even with that said, and even moreso acutally, power would be the way to go. You would get the most recharge out of it, because seriously, I'm a 4x Warlock and I regen more than 2mp per tick.