Hi John.
There's a long thread on the 3.0 upgrade, which you might want to review. A lot of it is historical speculation, but interesting to watch the progression from announcement to the reality of delivery. They're different.
The currently available 3.0 upgrade is only the battery. Not a small thing in itself, but also not the whole package as originally envisioned. The aero upgrades, tires, bearings and brakes, etc. are still being awaited. We all understand the concepts, and even have suggested some off-the-shelf options, but haven't seen anything endorsed or provided by Tesla that we can order.
I'd recommend you give yourself some time with the Roadster, to understand how it fits within your driving needs, and what options you have for charging. There are two big reasons to get the 3.0 battery, at least as I have it boiled down: 1. You need the extra 100 miles of range to enable you to do something you can't practically do otherwise (emphasis on practical - there are always charging options, but often they're not ones you can count on or exercise within the logistics framework of the trip). or 2. Your battery is shot and you might as well get the big one instead of repairing the old one.
In reverse order, Tesla has stated that long term, the 3.0 battery will be the replacement option for those needing new batteries. It's not something you need to jump on right now (emotional needs not withstanding). But if your car does need a new ESS (doubtful), that could be something to do now. I don't think it will give you a 1:1 increase in resale value, but certainly would be of significant value to the right buyer. 20k is probably as good a guess as any.
But the big criteria, for me at least, is the first one. Would it enable you to do something you can't do otherwise? For example, 99% of the trips I take are local, mostly back and forth to work. No problem there. But the radius of trips I might like to take include traveling to my daughter's place, which is just outside the current range of my car. She lives 214 miles away, according to Google, and my car's Ideal Range-mode range is down to about 220 (the car has 37k on its original battery). So, unless I get a charge along the way, I can't quite make it there, and worse, the return trip is uphill, so that's definitely too far. BUT, if I look at the overall trip logistics, I still need to charge the car at her place, and she only has a 120v outlet in her garage. Yes, there are probably some Level 2 outlets at a shopping mall, but that's still a 7 hr event, and probably not practical. With either battery, recharging becomes a multiple day exercise, and unless I take a day or two off work, that's not going to fit. So, the new battery wouldn't actually enable the trip. Now, when I retire some day, that might make sense, so the money is being saved for a future purchase. Just don't need it right now.
Hope this helps,
Greg.