Not so sure. People are greedy. I think the attack would work (although I guess we will not see such an attack in the near future).
For example: Upload a modified Bitcoin client which accepts a bounty of 500000 BTC per block starting from a specific block. Rent Amazon and Google hashing power and produce some 20 blocks faster than the Bitcoin community does. During this time, produce 500000 BTC per fresh block and pay a large number of bitcoin addresses some extra Bitcoins (as a kind of bribery...). Then reduce the bounty again to 100 BTC per block (or, different approach, 50 BTC) and distribute the information on what you just have done to many forums.
Now there is this interesting dilemma: If a user/miner adopts your software and the new block chain...he gets a share of the extra coins. If he does not...he will not get a share of the extra coins. Of course you will also get a big share of extra coins. I am not so sure how many users will stick with the old block chain and not be tempted by the extra share they might get ... if they switch. (Of course, getting the modified software to accept the modified blocks is not a trivial engineering task - but it can be done).
You are confusing this thread with your thread. Is this confusion intentional?
What you're talking about is getting people to replace their Bitcoin software with software the validates some other rules. This is totally orthogonal to attacks involving large amounts of hash power.
The alternative chains we saw thus far were based, to the degree I know and IMHO, on changes which did not produce visible benefits to the user and thus were not able to activate the greed reflex.
They have _all_ been 'beneficial' to their users in that by participating in them you're one of a much smaller set of miners, and thus getting a far larger percentage of the total produced coin than in Bitcoin. This is more extreme in some chains than others for example LQC had block rewards starting at 1000 coins and then dropping 4% every 1000 blocks or so, while Litecoin has payout's much more similar to Bitcoin but a single person could pretty easily be 1% of litecoin's total hashrate.
I have intentionally not responded to your thread because other clueful people have responded and you just keep continuing the boring debate. Please don't spread it to other threads.