About the current gifts:
Towels -- Okay, but nothing special
Pins -- Ugh, straight to the trash can
Tote bags -- I have not seen them, thus I have no opinion
I think they should consider:
Echoing what many others have said, they should offer any available upgrades to returning cruisers -- but it should be clear that this would only be if the upgrades were available -- I can't see making it an automatic thing, or it would raise the cruise prices.
Offer advanced Palo and spa reservations. Unless I'm really missing something, this would cost Disney nothing! They're already paying people onboard to take the reservations, so there's no difference (or at least little difference).
Or open Palo and spa reservations ahead of time for ALL cruisers, but allow returning guests a two week head start so they'd have a little advantage.
Allow returning cruisers to choose their dining rotation.
Offer more shipboard credits to returning cruisers. Because of the high mark-up on this such as drinks, this doesn't cost them much; however, it makes the guests very happy.
Open the booking dates to returning cruisers 2 weeks ahead of the general public. This would give returning cruisers a better chance of scooping up the coveted Category 1 suites.
If they want to continue giving an actual gift in the cabins, I think polo shirts would be a wise choice. Unlike beach towels, people will wear them out in public -- and all advertising is good! To avoid sizing problems, they could give a coupon good for a free polo shirt. The guest could go to the gift shop to pick it up.
Another good gift would be a coupon for free photographs in Shutters. This would cost Disney very, very little -- but most people love the pictures, and it'd get people in there where they'd likely buy more.
Coupons for free drinks or free arcade cards would make people happy and wouldn't cost much.
I would have no interest in:
Advanced boarding. Many people fly in, and they'd miss out on this perk anyway. I thought boarding was easy enough.
Cocktails with the captain type parties. I didn't enjoy the large group activities onboard (such as the Sail Away party), and I probably wouldn't attend anyway.
Why I think Disney doesn't do more for returning customers:
First, they won't offer significant discounts because -- duh -- we're willing to pay full price now. Why would they accept less? If the ships stop filling up, we'll see discounts.
They don't want to make the first-time cruisers angry or make them feel less important. Let's face it, this is a fine line. If you were a first-timer who was dying to go to Palo, and you found out that all the spots on your 3-night cruiser were already grabbed up by returners, wouldn't you be a little miffed?