If you are handy with this sort of stuff it will save you a bunch of money. I bought two 30A Siemens Level 2 units on eBay for an average of less than $175 each. Did the wiring myself. Level 2 charging can be beneficial if your electric utility offers time-of-day rates that can be cheaper if you take advantage of the rates during a certain (short) period of time. Also, if you often put more miles on the vehicle during the day than what your range allows, it may work that you return home after doing the first half of your errands, charge up again (in two hours) and then do the rest of your errands.
So while a Level 1 may suffice for many, there may be some advantages for you to get a Level 2.
Yes as I said "Some people can upgrade to level 2 for much cheaper". You are confirming my point. But I submit that most people are not able or willing to wire their own 240V outlet. Nor are most people going to buy used EVSE's. It's a good suggestion and I'm not saying there is anything wrong with it, I'm just saying that I think your experience is more the exception than the rule. Also not everyone is comfortable with the idea of using the OEM cable with an adapter to use it on a 240V outlet. I think it's no problem, I'm just saying not all owners will be comfortable doing that and will instead purchase a level 2 EVSE, which will also have higher capacity than the 12 amp OEM cable.
I also said "There might be occasional times that you don't have enough time to charge and wind up using some gas, or more gas than you would have if you had been able to fully charge. But for most people using level 1 that doesn't happen very often". You gave some good examples of when it can happen, but again I think for many people those are exceptions.
I have a time of use plan, but I have found that very few people do. I get basically half price between 11:00 pm and 7:00 am every night. Some TOU plans are shorter hours, but I don't think by much. I am able to do nearly all of my charging during those eight hours. Sometimes I have to charge during regular hours, but in the big picture cost wise it's not a big deal.
Most people don't calculate their electric rates correctly because they don't include tax. My utility advertises that their TOU plan overnight rate is 0.015 compared to 0.06 normal rate, basically one-fourth the price. However when you calculate in all of the taxes the actual overnight rate including taxes is 0.05 compared to 0.11 normal rate. So about half price. Still good, but not as much of a savings as they make it sound. Also with my TOU plan I get hammered with a rate including tax of 0.33 weekdays from 2:00 pm to 7:00 pm during the summer, basically triple the regular rate. So I have to try and avoid using AC in the house during that time or else it wipes out any savings from charging overnight. To manage that I prechill the house prior to 2:00 pm, but that's not something everyone is willing to do.
I can only do about 2/3 of a full charge during the eight hour overnight rate period, but very rarely do I need to charge from 0 to 100 in one night. But I can if I need to, it just means that only eight hours of that charge session is at 0.05, the other four hours are at 0.11. Four hours at 0.05 is twenty cents, four hours at 0.11 is forty-four cents. So when I have to charge from 0 to 100 in one night I pay about twenty-four cents extra for that charge session compared to if I had level 2 and could do the full charge within the overnight rate period.
Your example of arriving home in the afternoon with 0 EV miles, then going out that evening and not having enough time to charge, yes that can happen. But I think for most people not very often, and when it does the evening drive is probably only a few miles, to the store, to the movie theater, restaurant, etc. Let's say the evening drive is 20 miles round trip and you are only home for an hour prior to that. One hour of level 1 charging will add about 5 miles of EV range, so that means you will be using gas for 15 miles that evening. With gas prices and electric rates in my area, those 15 miles will cost about fifty cents driving electric, and one dollar driving gas, so a fifty cents difference that evening if I have to use gas. Of course different parts of the country will have different price scenarios.
Twenty cents here, fifty cents there a few times a month, it can add up, but I think for most people it would take a long time to recoup the $500 typical investment in level 2 charging. But everyone's situation is different. Someone who has a long commute, a time of use plan, and goes out most evenings, and who can DIY their 240V outlet and buy a used EVSE or use the OEM charger with an adapter, sure they will benefit from level 2 charging. But keep dropping those items off one by one and the savings start to disappear, and at some point level 2 will actually cost more. I still maintain my opinion that most PHEV owners will not recoup their investment in level 2 charging. But then again some will.
However even if you don't save money, level 2 is nicer to have than level 1, and that's a good enough reason if someone will enjoy their car more by having it. The reason for my post was just to dispel something of a misconception that many new owners have that level 2 is a necessity. You often hear of people starting to install 240V outlets even before they get the car. My recommendation for new owners is to go the first couple of months with level 1, then decide if you think you need level 2. A large number of people find that they do fine with just level 1.