You would need to have a relatively significant hash rate compared to the pool overall to impact the luck on the pool. Also, as you stated, it would take a while for that impact to be noticed. It just seems to me that taking such action would prove to be more detrimental to you than it would to the pool. As a mechanism to prevent a pool from gaining 51%? I absolutely cannot see adding a significant amount of hashing power to a pool that is already flirting with the 51% mark. Again, unless you have a significant portion of the hash rate of that pool, your attack would not be viable. And if you did have a significant portion of the hash rate already on that pool, you could simply move your miners somewhere else.
Assuming that the ~15% drop in recent bitcoin valuation was due to GHash exceeding 50% of the total hash rate (and who knows how much further it may have dropped if that abuse were not terminated), then you would need to lose 15% of your payouts in order for it to hurt you more than performing the attack. A drop in mining revenue well below that number would already cause a huge number of miners to switch pools, which would accomplish the objective of reducing the hash rate at the offending pool.
I did not mean to suggest that the individual miner could pull of a successful attack single-handed (with a couple of notable exceptions). But rather that community action of this nature would have a large enough effect in aggregate to get the job done. If the community reaction to this abuse by GHash is anything to go by, it seems plausible that a large number of miners might participate in such an attack if it were easy to do.