1. If you know you don't need a REX and $7k is a lot to you, I highly recommend looking at the i3
BEV for a fair comparison to the Leaf. There's a chance you won't find anything b/c $14k is pretty much the cheapest. At that price range, you may not see any savings from getting a BEV vs a REX. Maybe you already did that research and that's how you came up with your specific i3 from that link.
2. I suspect you'll keep the car for awhile. There won't be much resale value in selling it prematurely. The value you'll be getting is not monetary. The value will be the full use of the car itself, the experiences you'll have with your wife and guests who are lucky enough to ride in it.
3. You'll always be taking a risk with an EV. There just hasn't been enough history with EV's to really say for certain much of anything. The battery on the i3 has an 8 year warranty. For the Nissan Leaf, it's 60k miles or 5 years. With an 8k car, you'll feel a lot less of a loss if it decides to dump vs the more expensive i3 and may care more about the warranty coverage. Something to consider.
4. One big thing you should consider is the servicing of it. The i3 may have a maintenance warranty where you are. You'll have to check it b/c I think it depends on your area. One the maintenance warranty ends, you'll need to pay out of pocket. It may be good to ask about pricing. Just call a couple dealers and find out. I called BMW today on the way home from work and they quoted me $160 to change the oil and $190 for brake flush. Prices will vary, but it gives you an idea. I'd recommend calling around for Nissan and BMW for a real comparison for you. More can go wrong with a REX model. So if you really don't have any intention of using it on your short commutes, you may not want it even though the REX feature may be free for low mileage 2014 i3's. A BEV will be quicker off the line. 0.8seconds faster. No plumbing from a gas vehicle to worry about.
5. I would expect the i3's brakes to last significantly longer than the Leafs. I have no proof of that, but based on the i3 having the strongest regenerative braking system, you'll use the brake less frequently (unless you're having so much fun zipping around that you drive it more aggressively than you would the Leaf.
6. The mindset for my dad's friend which I never really considered until after he told me is that he doesn't mind buying high mileage cars b/c his commute and use of the car is so few that it'll still last him years and years. So it's not necessarily a bad thing to get a high mileage car in your situation where your daily mileage expectations are low.
7. You said you're looking more for reliability than excitement. I find the older I get, the more excitement I want. Sounds counter intuitive. You might be the same way. Be honest with yourself. Drive both cars and give points to the one that gives you the biggest grin.
8. For a number of reasons, the deals on the 2015 CPO models are the all around best value. They're priced so low by the dealers that you don't get much discount off private sales. It's very unusual to see such a huge boost in inventory coming all at once for a car. In this case it's 2015 lease returns. Dealers are trying to get rid of them more than private sellers are trying to rid theirs.
9. What makes sense on paper is what it is. Don't forget your heart and what just feels right. I wish you good luck in whatever choice you make. Glad you're looking into EV's. It'll be an exciting experience either way you go.
10. One last thing. If you ultimately decide on the Leaf, you may want to wait another couple months. My friend just took delivery of the 2018 Leaf. I haven't seen any on the road. It's quite new. When we start to see more of these new ones on the road, the prices of the Leaf you're looking at may drop even further. Perhaps worth the wait depending on what's driving your timeframe for the purchase. You do run the risk of the new Leaf drawing more attention from consumers adding to the bunch looking at buying a Leaf and they end up being your competitors for the older model b/c the new one is too expensive. I would still wait on the Leaf unless you see on with a rare trim option combination that you want to snatch.