Worth is always such a subjective call....what is worth it to one person might be totally unnecessary to others. That said, I will give you my two cents on the subject anyway

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Full disclosure, I'm a "picture person". If I come home from a vacation with nothing more than photos of the memories we made, I am a happy girl. Pictures are a tangible way of hanging onto memories long after the moment has passed.
We have purchased the photo package each time we have done the dolphin swim. The photographers are right in the water (so they are close enough to get perfectly centered and close-up shots which are taken directly on and not from the side) and the quality of the pictures is excellent. We always get lots of different pictures (including individual ones of each person
and family shots where we are all together with the dolphin) as part of the overall package. You will have both posed photos and "action" pictures (kissing, "swimming", etc.) from your swim.
I love the fact that the package includes ALL digital images taken that day, so I don't have to pick and choose. Selecting just a few will be much harder than you think it will be.
The quality of the other items included in the photo package is excellent as well. The largest package option has a leather photo album that specifically designed for the unique 6 x 8 print size that the SeaWorld parks use. The poster is pretty cool too, and they package it nicely in case you are flying home. I think we also got a frame as part of the package the last time we purchased it, but don't quote me.
The DVD I'm not too worked up about, but I don't like watching myself on TV

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If you have any other photos taken by DC photographers within the park, they too will be available to you as part of your photo package. You can find photographers in places like the aviary and wind away river, if you time it right.
Stuffed animals vary in price depending on the size you want, but we find them pretty reasonable. I think the smallest ones are about $11.95 plus tax, while the larger ones are between $16.95 and $24.95 (the bigger the price, the bigger the size). They have HUGE ones at SeaWorld for around the $40 mark. In addition to dolphins, the gift shops will have stuffed whales, otters, sting rays, etc.