Between park entrance and redeeming FastPasses, you'll be scanning your ticket 4-8 times a day (depending on how many extra FP's you make each day). There's also PhotoPass where you can scan your park ticket to link your on-ride photos, but only one person has to do that.
The Band is useless for things that are only available to on-property Guests like room charging, room key, dining plan, etc.
If you think that the cost per Band is worth it to your family to not worry about those 4-8 scans per day, then go ahead.
Personally I don't think the convenience is worth it to buy Bands without the extra things it does for on-site guests, but that's just me.
If you're in the area with a rental car, you could check out the Disney Outlets. I just saw in a YouTube video that some of the older style Band designs (that were originally $20+) are on clearance over there for $2 each.
-Rob