While there aren't any special checks on transaction data (yet), just fetching it means someone could be checking it, and deters any possible abuse.
Put another way, are you going to rob a vending machine if your bosses are all standing right there, even if they're not specifically looking for foul play at the moment?
It's already actual, since pools can't know who is or isn't verifying what.
Umm what? So you just said that there is no verification of the transaction data that GBT sends. So if there is no double checking, how is there an actual increase in security?
Say my boss installs a security camera by the vending machine, purposefully doesn't turn it on, and then leaves the room. We both know there's a security camera, but we both know it's not working. Is there an actual increase in security? Am I actually deterred from stealing? I would say no.
This is more like he installs a security camera, leaves it on, but "never" looks at the monitor/tape attached.
You really don't know if today might be the day he checks it...
You have yet ever to explain how having the transaction list is 'more' secure - other than to say "It is more secure" thus it must be ... LOL
Let alone how you could actually do anything with it.
The simple point is that if any pool does anything with 'bogus' transactions, you don't need a miner to see it ... any bitcoind can see it ... and the miner would need a bitcoind also ...
If the pool is giving you 'suspect' transaction to mine, it makes no difference until you find a block, but when you find a block those 'suspect' transaction will be there for everyone to see in the blockchain anyway.
But you have NO clear definition of what IS a 'suspect' transaction.
More the point, the reason why you haven't done anything with this data is simply that you cannot code up anything to actually do anything useful with it.
The check itself is a waste.
Basically it's some weird attack at pool ops - and we certainly know one ex-pool op who can't be trusted.