The exteriors of upper-story windows are among the more neglected parts of a home. They are definitely harder to reach, even with mops with extendable wands, and unless you want to clip up a very tall ladder, it's difficult to see if you've really gotten the window clean. Your other options appear to be to dismantle the window and screen upstairs or to just give it your best shot with that mop and let some dirt stay—but that last one really isn't the best option, as easy as it seems.
People Can Tell
People can tell when windows aren't at their most sparkling. Once you wash the window and let it sit for a few hours, dust will once again start gathering on the surface. But letting that dust build up is worse. Your house looks duller overall, and that impression spreads to the rest of the exterior. If you're trying to sell your house, dingy upper-story windows reduce that curb appeal, especially in a buyer's market. They look bad, and they make the potential buyer wonder what else in the house you've neglected to keep up.
Clean those windows, however, and people can tell that, too. Your home's exterior looks nicer, and buyers appreciate your attention to those little details.
Views Are Worse
Regardless of sales and curb appeal, people in your house won't have such a nice view if your windows are dirty. That might not matter if the view is of a neighbor's garbage cans, but if you have a better view, you want it to be clear and clean. A thin film of dirt makes everything look worse, and that's frustrating when you try to look at a sunset or far-off mountain view.
You Might Affect Your Luck
Not everyone is into feng shui, but if you're starting to dabble in it, get those windows clean. Dirt, unkempt windowsills, and shabby blinds are visual clutter and can block good, clean energy that should flow easily through the window. Fix the blinds, dust the windowsill, clean the interior sides of the windows, and have a window-cleaning company clean the exterior sides of the windows.
The cost for cleaning a typical second story's worth of windows varies by number and size of the panes, but it's more affordable than people realize. Have this done at least twice a year; four times (quarterly) is better, and monthly is fantastic, if you can fit that into your budget. Contact a company like A-Plus Window Cleaning to learn more.