Here's a poll to give you an idea of how many people do borrow points: http://www.disboards.com/showthread.php?s=&threadid=333179
As you can see, borrowing is fairly common, we do it all the time, no big deal. If you know the vacation you'll be taking on a regular basis, my recommendation is to buy the number of points you'll need for that trip up front. It'll be rare that you would find an add on for only 10 points or lesser amounts because there are title and transfer fees for a resale add on purchase which can total aproximately $400 that make the cost for only a few points too high.
Another option is to stay in a different hotel the night you come in - especially if its a weekend night. Some of us like to go back to our favorite non-DVC hotels (AKL, Poly). Others like to stay for cheap off site.
This will mean you may have points left over - which you bank for next year and you won't be 10 points short.