Just do the math when buying - we have had times (rare) when RCI forgets/doesn't bother to put the multidevice package on sale and two single device packages are cheaper than a two-device package.
Cruise fare prices are rarely discounted due Holiday "sales" - they get discounted because RCI needs to move inventory and it happens to line up with the "sales".
Folks have reported being able to get discounts (or perks added) on sold out categories (very rare), but you'd have to call and hope to get a CSR who knows what they're doing.
All ships have a mandatory drydock whose schedule is fairly easy to predict - what work will performed during those is a lot harder, but don't look for anything meaningful.
Right, in the planner RCI seems to have removed Surf - I think that is only for this week. The ships still have Surf and it will likely make a comeback in the planner as well.