The $100 offer is for new cardholders only (but you could certainly try to apply for a new Disney Premier card instead of upgrading your regular Disney Visa -- I'm not sure if that would work.)
I believe $50 is the most they offer now to upgrade. Log in to your current card and/or check your email to see if you have an upgrade offer -- I don't have a pop up on either of my accounts right now, but I do have a current email offer for $50 Reward Dollars if I upgrade and make 1 purchase -- but with the $49 annual fee, that's a wash. You do get 2 pts for Parks purchases, gas, groceries, and restaurants, but other cards pay better. (For instance, AmEx Blue Cash Preferred pays 6% on grocery stores, where I buy Target/Disney Gift Cards, get fuel points, and save upwards of 17% on my
Disneyland trips. Two of my AmEx cards pay 3% on gas....)
Best bet is to keep your current no annual fee Disney Visa and have other adults in the household apply for card with a referral bonus [I don't believe Chase will allow an individual to hold 2 identical Visas but I could be wrong.] The current offer is for a $200 Disney Gift Card when you get the regular Disney Visa (no annual fee) and spend $500 within 3 months. If they sent you a referral pamphlet in the mail and your household members (or anyone) uses your referral info, you will get $50 Disney Dream Reward Dollars on your own card.
Example: Husband applies with your referral info = $200 Disney Gift Card for him and $50 Disney Dream Reward Dollars for you. (And no annual fee on either card.)