Get Mr Tuffy tire liners. Note for winter riding smooth tires might not work in your area.
In general inspect the tires for slashing caused by glass. Look for slashes that go all the way through, are very long, ect. Also note that older tires while servicable pick up glass bits more readily than new. Exactly when you change tires is personal. For example if you are a group leader getting a flat is more of a problem than if you are just riding around the park alone for excersise.
Also note that Mr tuffy reduces performance.
2000 Montague CX, I do not recommend it, but still ride it.
Strida 3, I recommend it for rides < 10mi wo steep hills.
2006 Rowbike 720 Sport, I recommend it as an exercise bike.
1996 Birdy, Recommend.
Wieleder CARiBIKE (folding), decent frame.