We got the Silver Plan on our honeymoon and got really good use out of it. It's helpful to plan where you'll be using them to see if you're getting your money's worth. When doing this remember that each wish costs about $34 (kids wishes are cheaper, but I'm not sure how much) so you want each thing you use the wish for to be at least $34. So in general, dining is not a great savings unless you eat a lot, or go to the more expesnive restaurants. Cirque tickets, dinner shows, tours, and spa treatments are good savings though.
Also remember that all the wishes for your reservation will get lumped together, and can be used by anyone in that reservation. So it might be beneficial for the adults to use the wishes for meals, but not the kids. Then the adults can use the kids wishes for other stuff - Cirque tickets, tours, spa treatments, dinner shows, etc.
Another tip is to think about splitting you stay into two continuing ressies, and only adding the Silver Plan to one of the ressies. That way you'll only pay for the wishes you need, and won't be stuck trying to use up wishes in places where you can't get your money's worth. The only downside to this is that you have to use your wishes during the days of that ressie - they can't be carried over to the next one. It definitely takes some planning, but can be well worth the money.
Here's how we saved:
4 Day / 3 Night Ressie for 2 Adults:
**Hoop Dee Doo Revue (1 wish)
Regular cost (including tax and tip) is around $65
Total savings of ..... $31
**Spirit of Aloha Luau (1 wish)
Regular cost (including tax and tip) is around $65
Total savings of ..... $31
**Keys to the Kingdom Tour with lunch (1 wish)
Regular cost is around $60
Total savings of ..... $26 (plus lunch is included)
**Hidden Treasures Tour (1 wish)
Regular cost is around $60
Total savings of ..... $26
**Cirque du Soleil (2 wishes)
Regular cost is around $88
Total savings of ..... $20
So we saved about $134 each, or $268 for the two of us. You just have to do some planning, and figure in some math to see how it would work for you.