I can get the arms off my LEGO minifigs, however, will doing so repeatedly wear them out?
No, they are not meant to come off (and neither are their hands) and I imagine that doing so repeatedly will cause them to become loose, as is the case with hands.
I have noticed that the hands come off a lot easier nowadays compared to 1970s/1980s vintage Lego, but I'm rarely sadistic enough to rip their arms off :)
I did it regularly as a kid and, while it takes some effort, it had to be done a considerable amount of times for any damage to appear.
Removing arms allows for more variety in your minifigs, but also to use these elements separately for other purposes (never underestimate the usefullness of a single hand, or the architectural value of a torso).
Also, note that other arms have been produced (mechanical arm in the Agents theme, rock arms in Power Miners), so you can have interesting minifigs by using these. Same for boxing gloves recently released in the collectible minifigs serie.
One last thing - some minifigs are produced in China (for magnets, for example, or minifig collections) and there are some concerns about their quality, so you may want to be careful with these. Note that while the fact that they are produced in China (you can recognize them at the rectangle engraved in the arms) is a certainty, the fact that the quality is less good is subject for debate.
In my case, it depends. On older minifigures from the 80's, 90's, and early 2000's it's okay. (I'm not saying it's a good thing) Sure, doing it too many times will gradually wear them down, but not enough to the point where the torso or arms break. New minifigures from 2012 and onwards though, NEVER TAKE THEIR ARMS OUT UNDER ANY CIRCUMSTANCES! Newer minifigures tend to crack and wear out more often. I don't know why this is, but it could be a decrease in the plastic's quality over the years. (LEGO seems to be running cheap) Taking out the arms can (and will) cause massive cracks down the side of the torso piece. Just recently I got new Luke Skywalker and tusken raider minifigures from set number 75173, and BOTH of the minifigure's torsos ended up with giant crack from the bottom of the torso upwards towards the arm holes within 1 week of each-other. This crack causes the arm to loose support and come loose. I was enraged by this, and had to re-order the torso pieces. In conclusion, I wouldn't take out a minifigure's arms unless they are from older sets.
I used to do it as a kid all the time and not always gently, what happens after a long time is: a small crack appears from the "armpit" down, it's less of a crack and more of a "line" and the arms become a bit loose but I'm not that bothered by it because it's nostalgic.
Lego minifigures are in perfect condition only when they stand on your shelf.