You're right, but only because oil is the worst, most expensive way to heat a home. Pretty much anything beats it, except maybe electric resistance in places with high electricity prices. Wood, gas, and heat pump electric will all beat the pants off oil. That said, even 80% efficiency may be optimistic for a modern high efficiency wood stove. But even if that's overstated, as you can see, it's still a pretty good deal.
Additionally, your calculations may even be understating the advantages of a heat pump. 1.4 as the coefficient of performance is very conservative. I'd use 2, especially given how they not have high-efficiency units on the market than can deliver their rated performance at -15f. Some can go as high as 3 or 4 during periods of non-frigid outdoor temperatures and less than peak internal load.
Edit: you said, "Does that calculation make sense? Are heat pumps and wood inserts really that much better than oil? Can I really save 178 dollars a month by going with a 16 SEER heat pump?"
Yes indeed. But again, only because oil is such an awful fuel. Anywhere in the USA, one therm of oil heat is several times four times as expensive as one therm of natural gas heat, simply because of the relatives prices of oil vs natural gas. If you were comparing a wood stove and an electric heap pump to natural gas, it would get a whole lot more complicated--especially in the cases of a 95% efficient gas furnace, or a state with low gas prices or high electric prices.
No matter what you choose, do your wallet and the planet a favor and heat with something other than oil! It's expensive, it's dirty, and (IMHO) it contributes to awful foreign policy. Just Say No!
Edit 2: Some gov't verification of your numbers: http://www.eia.doe.gov/neic/experts/heatcalc.xls
This is a complex problem, and it's going to be difficult to provide an accurate answer without inspecting the equipment. So this is going to be more like a few comments, than an actual answer.
Water heater
I'll start with the water heater.
Old units aren't efficient
If the unit is older, it's likely not performing at peek efficiency, which is wasting energy. Updating the unit could save you money in the long run.
Tank heaters waste energy
No matter how much hot water you use, the heater is turning on from time to time to heat the water in the tank. The only way to eliminate this waste, is to install an on-demand unit.
Fuel source cost
Depending on the costs of different fuels in your area, switching fuel source could save money. Installing a gas fired on-demand water heater, could save you money long term.
Fireplace
If the fireplace doesn't have a fan, that is blowing heat into the home. You're quite possibly drawing more cold air into the home, than the amount of air the fireplace is heating. By using the fireplace, you could be blowing money out the chimney.
Also, the cost of wood is typically quite high, compared to other fuel sources.
Heat pump
Heat pumps use a lot of electricity, which in many parts of the country is an expensive fuel source. In temperate climates, heat pumps make sense because they're not typically used much. In climates where the temperatures often drop below freezing, heat pumps are virtually unheard of. This is because heat pumps aren't so good at heating homes, and often have to rely on supplementary electric heating elements.
Use the furnace on cold days
Since you have a gas furnace in the home, you can use that when the heat pump can't keep up. Depending on the local gas price, this could save you some money. In most dual fuel systems (like yours), if the heat pump can't keep up it shuts down and the furnace runs instead.
From your description, it sounds like the furnace and heat pump are running at the same time. This is not a good idea, and can actually cause damage to the system.
You'll want to configure the system (or have it configured) so that when the thermostat switches to auxiliary heat, the heat pump shuts down and the furnace kicks in.
Without actually being at your home, it's difficult to diagnose the problem. You might want to have an HVAC technician come out and evaluate the system, to help determine if you're wasting money.
Best Answer
Absolutely they will get better! Every year company's invent new methods of controll that have increased performance, research is on going to find better forms of "Freon" that are more efficient and don't have a global warming or ozone depletion problems. How fast will it happen? Right now there are small increments of improvement every year and who knows someone may have a groundbreaking discovery that takes us to a whole new level of efficiency. Would I wait to purchase a unit for my home? No I would do it now, well I did do it to my latest home not long ago. The advancements are usually small but continual as each of the big players try to be the best so if you wait 5 years the rating of the best units may improve 1 or 2 seer. 20 years ago 13 was a good value now we are getting above 20- 22 with many mfg's. Note seer is seasonal energy efficiency ratio. The higher the better. I use that instead of the coefficient of performance since seer is the standard comparison in the trade. To further answer your question we would need to know why you ask.