The line I was thinking of was "If it also assumes very specific answers to difficult philosophical issues ("reality exists independent of consciousness")[...] then there is not a lot of reason to consider it a useful philosophy."
Consciousness and its relation to reality is still very much a philosophical conundrum, just look at all the P-Zombie/teletransporter threads on this forum. To just assume one specific answer and use it as a "central tenet" is not going to produce very good philosophy.
(I seem to recall her acknowledging that senses can give inaccurate information, such as when someone is nearsighted).
The problem is deeper than just seeing reality a bit blurrier. By necessity the sensory mechanisms both throw away huge amounts of data, and fill in parts that are missing. You see things that aren't really there, and fail to see things that are. Despite what Rand claims, much of this is completely automatic. What she calls "volitional consciousness" doesn't even enter into it, if it is a meaningful concept at all.
But if reality isn't knowable then how can you even show that "some ideas are more difficult to prove untrue than others even if they are falsifiable"?
You could read Kuhn, Popper, Lakatos, or a favourite of mine Bruno Latour. Or you could read a bit
about them, their ideas are clear enough that you don't need to claim that their philosophy can only be understood if you read their own work. Even their critics seem to be able to represent them reasonably well. Only cultists claim that one can only fairly criticise their favourite philosopher's ideas if you slogged through their unreadable works.
Could you perhaps offer a concrete example where progress could be made while acting on the assumption that reality is unknowable?
Take Heisenberg's uncertainty principle; it states pretty clearly that some things about reality are ultimately unknowable. Once you accept that, it is actually pretty useful. There are also Gödel's incompleteness theorems didn't stop progress in mathematics, or the halting problem of Turing machines that actually started progress in computing. Or how about the fact that the observable universe is just a tiny part of the entire universe; according to some theories the observable universe may be similar in size compared to the universe, as an atom is compared to the observable universe. What's outside the observable universe is unknown.
Those show that some things about reality are completely unknowable, and they are just little problems compared to the big questions.
1. You assume reality is unknowable and are correct--the "train" passes through you and you are unharmed.
2. You assume reality is unknowable and are incorrect--you stay on the tracks and are killed by the train.
You forgot to mention:
1.5. You assume reality is unknowable and are correct--you step off the tracks and the train passes by.
2.5. You assume reality is unknowable and are incorrect--you step off the tracks and the train passes by.
Just because it is unknowable whether the train is "real" doesn't mean I won't move away from it. Whether or not the train is real, it may be just as real as I am. An imaginary train may very well run over imaginary me, ending my illusion of life.
According to quantum mechanics, there actually is a non-zero chance that the train passes right through you, though it is safer to bet against it.
There may be benefits to assuming that reality is unknowable and being correct, but there is a massive downside to assuming reality is unknowable and being wrong.
This argument is rather similar to Pascal's Wager.
I agree that even in an unknowable reality certain choices we make will still matter to us, but other choices will not have any context which we could use to determine the best course of action.
Then perhaps we should admit that for those choices there is no answer. That seems to me a more practical way of dealing with those choices than to assume there is a answer and declaring your preferred answer to be "objective reality".