Actually, for stats to work properly, they must have synergy with all other stats. For example: When I get more Spirit, I can cast more RJWs. But that RJW can multistrike, crit, and proc GotS, and is increased in throughput by Int and Versatility. GotS orbs can crit and multistrike. Crits can themselves multistrike. All of the stats have multiplicative synergy. Purposefully removing that, such as not making your Haste regen scale with Spirit, would actually cause Haste's stat weight to !decrease! the more Spirit you had.
Intuitively speaking, this is because the extra mana gained is a smaller percentage of your total mana (yet you're still gaining GCDs at the same rate). Thus, some of the extra GCDs you gain will still follow the current "mana-limited" model. For example, if half of your passive regen is from Spirit, then half of your new GCDs would still follow the mana-limited model, while the other half would follow the GCD-limited model, for calculating an average value. As your Spirit increases, a larger percentage of those GCDs would follow the mana-limited model, decreasing Haste's stat weight.
A better thing to do would be +0.5% regen from base and Spirit regen per 1% of Haste, or some such mechanic. That is, make it have Spirit synergy, but scale it down by some amount to keep it from being overpowered (like if it gave more regen than Spirit itself in addition to giving you more GCDs -- an obvious strict gain).
(For Crane stance Pool of Mists only)
Since RSK hits so much harder than BOK or TP, +1% GCDs from Haste doesn't work out to +1% damage, maybe instead +0.7%. Taking an equal amount of Multistrike rating instead would not only give you about +0.8% damage across the board, but it would proc additional Jade Mist procs for RSK, increasing your damage even further. Unless I'm missing something, MS is almost surely more powerful than Haste for pure crane stance with PoM.