We nearly always park-hop... virtually every single day.
But YOU may not NEED to.
How do you know?
What should you do?
Simple:
You don't need to buy the "Hopper Option" UNLESS and UNTIL you need it.
If you are already at one park and decide that you'd like to "hop" to another... right then,
just walk up to a ticket window, add on the Hopper option (costs the same price if you buy it before or DURING your trip) and you're ready to hop (that day, and any others, for the rest of your trip.) You must make this and all other upgrade choices within the first 14 day of when the ticket was first used and no later than on the day that you use the ticket's last asset.
If you go and NEVER need to hop, don't buy the upgrade, and you can then spend all those "extra" bucks on more WDW souvenirs!
The Hopper is a one-time charge that will cover every day on your ticket from the time that you choose to add the option.
The cost of the Hopper option now varies... as of the last price increase (Feb, 2014.)
If you upgrade some tickets by adding "days" you might also have to increase what
you pay for the Hopper option on those tickets.
Adding the Hopper to a one-day ticket costs $40.
Adding the Hopper to a two-day or three-day ticket costs $50.
Adding the Hopper to a four-day thru ten-day ticket costs $60.
SPECIAL NOTE:
If you already have the Water Parks Fun and More option on your tickets,
adding the Hopper is a one-time, one-price fee of just $26 per ticket.
All prices, plus tax.