I think the other posters here have covered the points pretty well... but I'll throw in my $.02
Motions require the person to really physically be in the house - where glassbreaks will catch them when they first break the glass... Usually once they break the glass they have to clear out the frame so they can safely enter without getting cut to shreds - and that takes time. If the siren goes off the second they throw the brick, they're out of there - but if it doesn't go off until they're standing in your kitchen, they'll likely at least grab the laptop sitting there on their way out. More importantly, if someone means you harm, by the time they're in they could just put a gun to your head and tell you to disarm it; whereas if the alarm goes off before they get in, hopefully they don't get that far.
Homeowner's insurance is great for protecting your valuables - but I've never heard a break-in victim complain "Oh, I can't believe they took my Sony TV!!" - no, it's the feeling of being violated - someone in your home, going through your stuff... not knowing what all they took, or what they learned about you in the process... or if they take the computer with all your family pictures on it (True story: I have a sister many years younger than me - her birth was filmed and the tape was in the camcorder - someone broke into my mom's house and took the camcorder, with the tape - nothing else... 15yrs later that still bothers everyone in the family). It's rarely about the money at that point.
If you're worried about being able to open windows at night, there's 3 options. 1. Get security screens - they work by protecting the outside of the window - if they're removed or slashed they trigger; you can still open the window independently (great option; pricey). 2. Bypass the window zone (open the windows for the night; arm before bed bypassing any open zones). 3. Use two magnets - It's not uncommon to put 2 magnets on the window - one in the closed position and one open about 6" - you set it at the 6" position and arm - and if someone tries to open it more (to climb in) it triggers.
As was said above, the hardwired sensors are only about $1.50-$3.00/each - and wire is cheap enough... That's one thing you can't go back and do later and you can't go wrong doing it now. As far as maintenance, hard-wired sensors can work for a long time. In a 30yr old house you'll often find all the sensors working great; worst case may have one go bad - and they're easy to replace. Done right, all hard-wired, the only maintenance you're looking at is the alarm battery (and doing a walk test occasionally just to verify proper operation of the system).