For the cooling attachment to break it is more likely a manufacturing fault; probably there was some tiny scratch/crack/internal stress that propagated.
Increasing power doesn’t alone require replacing the whole machine, though power is basically a function of tube length. If your cutting area is big enough, you can upgrade for very little more $$ than just tube replacement.
You can get a higher-quality tube than probably came with your machine for a reasonable investment. Lightobject (35W / 40W) and Cloudray both sell high-quality tubes. You’ll need to check the length of the tube vs. your machine; you may need to also get a case extension to put in a true 40W tube; that extension will let you go up to 1 meter long (50W). You’ll need to consider whether you need a new laser power supply depending on what tube you get; the supply you got with the unit might be good up to 40W but not beyond.
See also