This is not a cabins becoming unavailable issue - this is likely just normal inventory management. Sometimes the whole sailing could be taken offline for inventory management. Eventually, inventory comes back.
Invest in a blow up Klymit or similar topper - they take up very little space. You can never count on any soft mattresses on RCI and no, Jewel didn’t get any better after her dry dock.
Unless you got it for about the same price as the internet package, most folks see little value in the rest of the perks. You can cancel till three days out.
The cabins sometimes become unavailable as late as turnaround day. During COVID days this was normal as RCI would take the cabin of a COVID positive customer out of service for the next sailing. Many other things could take a cabin out of the inventory.
While very rare, folks have been bumped on oversold sailings- folks with a GTY booking might have a slightly higher chance of being bumped in such a scenario.
Go to one of the speciality venues upon boarding and while you are making the UDP reservations, also make one for Chefs Table and cancel your existing one. You should get refundable OBC for the cancellation.
As is the usual recommendation, unless you were going to buy a Voom package and it’s close in price to that then Key might make sense.
For the couple of issues you mentioned, it probably doesn’t (no discount on room service). You can probably buy lunch at a specialty venue on boarding day and Voom for less than Key.
No, everyone usually has the same arrival time options. Again, that’s likely an IT glitch which for this discussion makes no diff as at most ports arrival times are not enforced.