I definitely don't understand Disney's rules and structure to a "package". Anywhere else, you'd usually expect a package to save you some money, but at Disney it's just souvenir luggage tags, some discount coupons for things like boat rental, fishing, mini golf and I think one restaurant at DTD. Then you have the longer window where you have to be paid in full. I often get the dining plan, so I book a package, but I don't see any other real benefit.
if a discount becomes available, you can still call to have it applied to your reservation; if you booked a package, but the discount you want is a Room Only, they can convert your reservation and get you the discount. I guess if the discount you want is free dining, you may not want to buy tickets elsewhere - when you stay at a Value, the free dining discount is often more $$ than a room only discount, but it requires purchase of a hotel stay plus tickets. If you purchase offsite tickets now, and later want the free dining, you'd have to buy yet more tickets, possibly negating any savings.