Doesn't make sense to establish a limit on spacebar/arrow/etc. sensitivity, because there's no standard kb with standard sensitivity, from the start of WA we've all been using different kbs with different amounts of responsiveness. Sensitivity of the keys seems like a parameter we should be able to tweak as much as we like, since there's never been any disagreement that it's fine for it to vary significantly from kb to kb.
In terms of visual aids though, it's not something we started with much agreement on, and it seems like most people are against them. And yes, you can't use visual aids currently. We certainly could allow them, but they ruin BnG (even further), and in other schemes allow people to write down information, use transparencies for distances, etc.