Depends on when you are going. Weekdays are not generally packed but sometimes during the summer around holidays.
The all you can eat dining plan is great if the park is open late such as 9am-10pm. That allows you to eat breakfast, lunch and dinner making it a great value. On short days of 10am-6pm it may not be worth it.
Ride lines are usually not bad at all. I rarely see lines of more than 10 minutes except for Shipwreck Rapids on a hot sunny day which can reach 45-60 mins or on the bayside skyride in the evening which can be 30 minutes. Journey to Atlantis and Artic Adventure rarely have long lines. Manta varies but is rarely longer than 20 minutes with shorter being more common.
Shows are not a problem. Just arrive 15-20 minutes early and you'll have a good seat. Arrive 30 minutes early for the sea lion show as they have a pre-show which begins 15 minutes prior to posted show time.
If you plan to go to Seaworld another day anytime in the next year it would make more sense to buy a Fun Pass at $79. The dining plan can be purchased at the park separately.
If you do not get the dining plan at least buy a souvenier refillable cup which starts at about $10. This allows you refills for about $1.25 and can easily save money. Cup can be brought back on later trips. We bring 10 year old cups and they still allow the refills with them.