When deciding to get a hybrid for my wife to drive, one benefit that out weighed the gas mileage was the range between fillups. We knew that it would take a long time to recover the difference in price between the comparably equipted gas version and the hybrid version, but the difference in the time & distance between fillups was a real draw for us. With my wife's old car (V6 engine), she was filling up every 10 days or so & going about 200-240 miles. With her new car, she goes 3-4 weeks easily & up to 600 miles between fillups. She really appreciates that, especially when the lines @ Costco could be 10-20 minutes long. The only thing I am a little concerned about is that I hope the gas doesn't go stale between fillups. That time in line to fillup isn't counted in the price difference, but is a benefit of the hybrid or any plugin/electric vehicle.
It would be a similar story if you bought a small diesel, although I appreciate the market isn't as broad for diesels in the US. I too used to fill up every 10 days in my old gas car, getting only 250 to 300 miles per tank. Now my current car only has a tank two gallons bigger, yet it gets over 700 miles per tanks and lasts 4 to 5 weeks.
I wouldn't worry about the gas going off, it would take a minimum of 6 months for this to happen I think.
The fuel tank of a car is also much better sealed than the one used to fill your lawnmower. So the car gas is losing less of the more volatile fraction and getting exposed to less air. Those are the main causes of gas going bad.
Hybrids are not all the same. As a comparison, check out the 2015 Audi Q5 3.0 V6 turbo diesel compared to the Hybrid, powered by a 2.0 inline 4 turbo gasoline engine. EPA ratings place the diesel as more fuel efficient except in the city, where the hybrid is only *slightly* better.
In real-world use, where gasoline engines don't do as well as EPA numbers and diesels do noticeably better, the V6 diesel is more powerful, more fuel efficient, less polluting, and considerably less expensive!
My Q5 diesel is expected to arrive at the end of May '15. I can't wait to see what kind of fuel economy it'll deliver.
My take on diesels is that they are a better choice for steady rate usage (i.e. freeway drives) than stop & go city drives. VW's diesels gave a 600 freeway mile range, the hybrid gave 600 city mile range. Since my wife's daily drive is 10 miles each way to/from work on city streets only, a hybrid seemed a better choice in our case. Ideally, a plug in EV would have been the best option, but since she occasionally drives a freeway trip on the weekends, the EV anxiety of running out of juice was a real possibility. The plug in hybrids we looked at seemed to be a possiblility, but the best balance between our usage, performance, and price made the conventional hybrid our choice. The last factor was that most of the diesels that we would have considered came from manufacturers that had spotty reliability records, VW/Audi being the front runners in our choice of cars. We waited for Mazda to put out their SkyActive-D engine last year, but they delayed it indefinitely. Trunk space was never an issue. Except for the occasional road trip in the past, we never really filled a conventional trunk to capacity in our entire driving lifetimes (once we got out of college). If we take road trips that require a larger trunk, we rent a vehicle now.
And you're right about the diesel market here in the US, at least here in Calif. Within 3 miles of home, there is only 1 gas station that carries diesel, so there isn't any incentive to keep diesel prices down. It's usually more expensive than premium gas around here. On the other hand, within 2 miles there are 3 Arco stations and a Costco (plus a couple of independants) that all compete to keep gas prices low. So diesel access also factored into our decsion.
As far as the gas stability issue, my concern is the Ethanol factor. I've heard it separates out over an extended amount of time and I'm not sure what that does to the overall health of the engine/fuel system. We have 10% here with some places going to 15%.
Ethanol only separates out when enough water gets into the fuel for phase separation. The normal amount of water that gets into a tank through condensation isn't going to be enough. There needs to be a leak letting in rain or car wash water, or it comes in during refueling.
Gasoline sitting in a properly working fuel tank isn't going to spontaneously phase separate.
Plug in hybrids that have a large ratio of EV miles are the only cars that might have to worry about gas going bad with regular use, and then the manufacturer took that into consideration in the design.