I was on the fence as well, this past August. I ended up cancelling the package because we had too many ADR's as it was. We went on a "7" day and I thought that it was only a "7" at Fantasmic! It worked out for us in the long run, but there were moments I second guessed myself.
We arrived late afternoon. Rode some rides, had dinner at a CS. It all was going as planned.... I began getting nervous when it started storming (with intense thunder and lightning!)

then the park started getting really busy close to Fantasmic show time. Then a line started forming which spilled out onto Sunset Blvd. We queued up and stood in line "forever" in 10 year old boy time (about 15mins). Once the line started moving there was a line beside us which was roped off and obviously meant for CM's but ds (10) was sooooo upset because he kept seeing guests use it (some to bypass the crowd, most to meet up with the rest of their parties - maybe some had packages

). Anyway, ds did not like seeing that

If they could use it, why couldn't we!!!! He kept wanting me to tell them to get in line like the rest of us. I just kept trying to destract him so he didn't start some sort of ruckus.
Once we navigated the line (which took another 15mins) we were seated nearly front row with an awesome view of the entire show and we waited another 15 mins for the show. In all from getting in line to show time we had about a 45 minute wait.
I don't know if this helped, but I think it comes down to how important the show is to you and whether you are willing to gamble on it like we did. We did fine without the package but it really could have gone either way. We have seen it standing, as well..... and that was not as fun.