So my dealer gave me a ~$7,500 discount on the 1958 but is willing to buy it back for $1,000 more than what I paid. And they're also willing to do a $7,500 discount on the Premium that they have in stock. So to upgrade, I'd have to spend essentially a $1,000 or so less than the actual spread in MSRP + TTL/fees, so around $12k all in with TTL/fees.
This is essentially their first offer, so I'll see if I can do better but if not, would love to get this forum's thoughts (particularly from those that have made the upgrade) as to whether I should do this. I plan on keeping this car for a long time (I still have a GX460 that's 14 years old) and am thinking maybe some of these upgrades would be nice to have over all those years.
I know others have gotten better deals to upgrade, but this seems to be the limits of what I can actually get in terms of an offer with my limited negotiation skills.