I currently have a gold season pass. I purchased it during the MVP sale so I still have all park access, but would an upgrade to prestige be worth it nonetheless? Or would that money be better spent as a dining add on or something else?
To be clear, Prestige has never been an all-park pass, so the MVP sale doesn't do anything to negate its value. It's always been a park-specific pass.
Financially, I think Prestige is immediately "worth it" if you plan to bring two friends/family members to the park this year and would otherwise buy a day ticket for them. The two free bring-a-friend passes are worth about $60 minimum (total), compared to the cheapest bring-a-friend tickets you can usually get that are included with the gold pass; on a more expensive day, they're worth more like $90. So if you were going to buy those tickets anyway, that brings the "effective cost" of upgrading to Prestige down from $100 to between $10 and $30. It's even less if buy lots of merch of non-dining plan food and can stretch the extra 5% discount.
Beyond that, I think the biggest perk of Prestige is the VIP lounge, so if you find the free tickets valuable, then I say it's worth the upgrade for the lounge alone. I've used it as a work-from-home space a few times and totally would've used it as a place to do homework if it had existed back when I was in school! The free snacks are a nice little perk too, and I've saved at least a few dollars by grabbing those instead of paying for a snack in the park.
The other perks I could take or leave. The single-use Fast Lane is nice but I rarely visit the park alone anymore, and usually being the only person with Prestige, I often don't use it. The VIP entrance is nice but only available a few hours a day. Preferred parking is nice on crowded days though only marginally beneficial on lighter attendance days. The "improved" Pass Perks (which I think they've removed as a benefit, mercifully) were a joke; just a collection of BOGOs and other gimmicky sales on things like popcorn and pretzels.
Still, it's not a bad deal if you'll actually use the benefits, IMO.