I have experienced massive water flow in the sumps when they've been unplugged or just not running while water continues to build up around the foundation. If you have a lot of clean #57 stone around the footer, under the slab, and even up the exterior walls some, it will "store" water in the voids between the stone. This water can travel quickly to the sump when it is "stored" between the stone in this situation, which is precisely why the stone is used in the first place. Sand will do the same thing, but slower.
In torrential rains, you need to move a lot of water fast... and clean #57 or larger stone allows you to do that. Basically, the stone is a big pipe or conduit.... and water can travel both horizontally and vertically through it, so long as it's not infiltrated with sediment.
Is the "every 12 seconds" you speak of measured just after you plug in the sump? Depending on how much 4" pipe you have around your foundation, a gigantic amount of water can be stored in it. Eventually, though, the pump will "catch up" and all that stored water will be gone. Then I would expect that it slows back down to a more reasonable rate...even if it's still raining outside.
The time to be most worried is when the sump ISNT working. That's when you start to get differential settlement and buckling walls in freeze-prone areas.
Obviously, the soil needs to be graded away from the house (in the back yard). If that means you need a retaining wall, then you need a retaining wall.
Regarding the swale, improved drainage sounds helpful. The real question is, why isn't water shedding (what is the real issue)? I've had swale issues, and the problem in those cases, was not with my swale, but the neighbors'... so water backed up in my yard. In such a circumstance, you can talk to the neighbors about the issue, ask them to fix it, offer to help, and/or sue them for damages.
But if the neighbors aren't to be blamed, then another alternative to keep the grass cut very short (grass slows drainage). Or you could check into a trench drain (concrete ditch). This is just another option that I didn't see mentioned, although it may not be your best option. As Tester101 pointed out, being there to see the issue is probably necessary.
Regarding power outages, gasoline or propane generators are the most reliable answer. A moderate generator should be enough for a sump pump, the fridge, and should keep the toilet flushing too. As you know, the drawback with a battery bank is that once it discharges, then you don't have a simple solution, like getting more gas.
Edit- Here's a possible way to use a retaining wall to increase the grade away from the house.
Best Answer
There's typically a drainage system around the inside perimeter of the basement (perimeter drain), which feeds into the sump pit. If the pump is not removing water, the drains will fill just the same as the pit.
Water always finds level, so if it's above the rim of the pit, it's also filled the drains. So theoretically, water could seep in anywhere around the perimeter of the basement.
Once it's found a way in, it could fill the basement like a pool.