I have 2 Dremels and a Foredom, use one Dremel most, and keep it on the bench, plugged in. For a decade, it was my most abused tool, used way over its expected abilities. Cutting off toilet bolts to length, removing screws, slotting screws, scoring scraper blades, grinding blades, increasing hole sizes, even sanding occasionally. Now the OMT takes the worst abuse.
The skinny cut off wheels are fragile, and the off brand ones are worse. Buy Dremel or Foredom brand, not cheap off brands, and they will last a little longer. The fiber reinforced ones get called out for the tougher jobs, where it may take 3-4 thin ones. The larger OD of the reinforced can occasionally be a problem, but I keep used ones for smaller access areas.
As Meursault says, technique will make the discs last longer. Keeping your victim and your tools relatively square makes a huge differences, if either is out, you will bind and break the disk. Learning to hold the motor so it doesn't swing in confined cuts will help. I've seen the equivalent of a miter saw made for a dedicated purpose, blades last longer, but they upgraded to diamond now, cutting glass repeatedly.