Hello and hope you do decide to join "the SE club."
IMHO, there is little or no way to reliably predict the value of these early MINI electrics in 3 years' time. There aren't many used MINI SE on offer around the country (or new ones, for that matter), so there isn't a whole lot of data to be found (although I am certain that you found one of the best places possible to ask your question of folks more knowledgeable than I).
That said, however, and first, it is perhaps the least expensive full-electric vehicle on the market in the US today, so that helps mitigate the financial risk quite a lot up front. Second, this significantly lower cost of entry for an otherwise really fun driving city car also has great operating economy among even EV's in general and carries through to prices of insurance, etc., saving you even more $ over time of ownership. Third, in CA there are other unique advantages to be had, including state, local and utility rebates for which you might benefit, and even the HOV lanes are open to EV's making your commute a little less of a hassle.
New MINIs qualify for the full $7500 federal income tax credit and a federal tax credit on purchasing & installing an EVSE (a charger) at your home.
On the downside, I would say it is very likely that BMW / MINI will in the next few years introduce MINIs with better batteries, longer range, etc.
If you want to really hedge your risk, you could consider leasing an SE too.
My (adult) son lives in Venice Beach (next door to Santa Monica), and his usual drive car is now an older ICE (internal combustion engine) VW Golf, but he also is thinking about a new MINI too.
Anyway, good luck with your decision-making and hope to see you soon and often again on this forum.