Get the FP for TSM.
When are you going? Currently, Frozen is interfering with the ability to go to TSM at rope drop like you would have been able to into the past. They are doing a similar process as at MK with Anna and Elsa and mine train. So Unless you are at the front for rope drop or go late at night, the standby line will be long.
The dining package for Fantasmic is a great option, but it is only offered at Hollywood & Vine, mama melrose's and Brown Derby. Most people here and CMs will say a Fantasmic FP is a waste. If two shows are offered, go to the later one. If not, you will need to get in line early and wait, but you can sit, eat dinner in line, etc. honestly, I've never had a really lousy seat at Fantasmic so you should be fine. But if it's important to you, just wait in line for around an hour, hour and a half before they open the theater.
Forgoing a TSM FP is a huge mistake, especially for Fantasmic, IMO.