Don't upgrade to no expiration unless you really plan on not using all the days. It's so expensive. For a 10 day pass.. you're paying an extra $240 dollars per adult for no expiration. For only $30 more you can get an AP and get all the AP discounts and a lot more days for your next trip if it will be within a year. The AP will be worth the discounts alone for at least one member of your party to buy that.
We had annual passes several years ago and did 4 WDW trips (20+ days at the parks) that year. The AP is great if you are going to spend a lot of days at WDW during a 12-month period.
Having just purchased a Universal annual pass (at 1/3 the price of WDW AP), our first DCL cruise planned for later this year, plus a few days left on our current WDW tickets, I am confident these 10-day no expiration tickets will last several years.
Unfortunately, WDW has increased ticket prices at double the rate of inflation for the last several years and I want to purchase these before the next price increase (usually August). These 10-day no-expiration tickets are going to cost at least 50% more than what I paid for the same ticket only a few years ago. With hindsight, I wish I purchased more tickets then. I'm having a hard time paying $626 for a ticket that cost me at least $200 less only a few years ago but am afraid if I don't buy these now then these same tickets will soon be over $800! Don't laugh; I never thought 10-day no expiration tickets would cost more than $500, never mind $600.
If we plan a longer trip (5 days or more) we'll buy tickets for that trip separately and save these 10-day no-expiration tickets for our shorter visits. Per the disneyworld ticket page, these tickets work out to $62.60/day, half that if you include the 10 days of water parks. (We never use both a theme park day and water park day on the same day when purchasing the no expiration option.) Currently a 5-day park hopper (no water park and that expires) costs $61.20/day, a 4-day is $74.50/day.
A Premium AP (i.e. water parks) currently is $649 while a regular AP is $598. Doing the math, we'll buy an AP if we'll visit the parks for at least 10 days during a 12-month period. However, with our Universal AP and DCL cruise planned, I doubt we'll be at the theme parks more than 3 or 4 days this year (plus 3 or 4 more water park days) so a Disney AP doesn't make sense at this time.