Great! We have snowplows and icebreakers etc. on standby (almost) all year round, i.e. capital doing nothing. It's not a problem. And unlike snowplows and icebreakers, as soon as storage capacity is available, it won't be a financial problem: You store surplus energy to be used when there is no wind and/or sun. (Unfortunately, you can't plow snow or break ice in advance of snowstorms or sea ice.)
As it is, electric power is cheaper when it's windy and there's plenty of it and more expensive when there's little wind. When electricity is used for heating houses, that's pretty neat. During cold winter storms, electricity is cheaper.
But again, the main argument: Fossil fuels make the planet uninhabitable. The idea of using fossil fuels only now and then to make up for temporary shortages doesn't change that fact, and it is the number 1 problem that has to be solved. Wobs' example is good in this context: Idle windmills will be switched on when the demand rises and switched off when demand is low. The extra capacity needs to be there, of course.
And any source of power that is switched on and off can be considered to be on standby some of the time: "dormant wind turbines etc on standby." It is not specific to wind turbines, and it is as good an argument against all other sources of power.
Energy storage costs money. The more you install, the more the electricity you supply will cost.
Installing wind turbine/solar panels costs money. The more excess capacity you install (assuming you want to go 100% renewables), the more your electricity will cost.
With the intermittency of wind/solar, you would have to install a huge amount of excess capacity to compensate, and the bulk of that would remain switched off for much of the time, while you wait for weather conditions that reduce the output of them enough.
Lets imagine Tokyo relied entirely on off shore wind. They have a huge quantity of excess capacity of turbines, and battery storage for when the wind drops. Then a storm hits, and all those turbines have to turn off, as its too windy. So they rely on battery back up for three days. How much do you think they'll need? 14million, purchase price: $400billion, which averages out at $27billion per year. (Numbers from How to Avoid Climate Disaster by Bill Gates)
That's just for the batteries, not including the wind turbines, which would also be expsensive owing to the excess capacity.
Again, the more excess capacity you install (ie. those units you often switch off), the more you energy will cost.
Lets compare wind with gas (I would rather do away with fossil fuels of course, but its a useful illustration):
A grid of say 50GW might need 20GW* of gas capacity to deal with variation on a day to day basis. But if you were to replace all of this with wind, you would need far more capacity than that. In fact it would need to be many more times that 20GW, as it would need to deal with low wind for prolonged periods, too high wind for prolonged periods. And of course, given that turbines cannot produce their full rating for the majority of the time, we would need far more installed capacity. This is in addition to energy storage costs. This excess capacity far exceeds any capacity you would install with gas or coal.
Another example: In 2010, we had a deep freeze in the UK, where we had very little wind for weeks at a time, and demand was highest. The days were short, and coal was burned in abundance. To accomodate such a situation with renewables, would be completely uneconomic. You would need a capacity so huge that the bulk of them would be turned off for most of the year, not earning their keep.
Sure, we might get the odd day where people can go "Hey, we're running on wind, see it works!" but that ignores the reality of day to day needs, and the varibility of weather. I see people doing this on another forum I go on.
The excess installed capacity needed for fully renewable makes it uneconomic.
Its tempting to see the cheapness of wind/solar energy today, and extrapolate that to the full grid, but it doesn't work that way, and the study I reference yesterday confirms this.
In addition: we will need more electricity in the future, as we electrify more things (eg. steel manufacture and running cars), people install more aircon, and economies grow. So this issue is intensified.
Your snow plough analogy doesn't work, as they are relatively cheap, and the economic value of keep roads clear and safe are factored in. Also, here in the UK we don't invest much in such things as we rarely use them, compared with say Finland, where they are far better prepared, as they get snow far more often. Its just not worth it for us to have that level of preparedness.
* - numbers for illustration purposes only.
The problem with solar and wind is sometimes you won't have enough power, because for example its a still night... or its a stormy night (over a certain wind speed windmills have to be shutdown). The only issue with nuclear is sometimes you'd make so much energy some of it would be wasted? 
