Most modern shoes have a life in distance not really time. Running shoes are typically 300-500 miles and heavier hiking shoes will be more like 1000 miles. There are synthetics in the sole that break down over time and lose their ability to support you. So even if the sole/upper is in good condition the shoe could have failed because the sole is done. It is hard to tell this when you wear them normally but try them back to back with a new pair and you will see this. So for something used as heavily as you are say you are using, they likely will only last that long regardless of how much you spend. The only way to get a longer lasting shoe would be to go to something made in a traditional way with no synthetics but you lose the immediate support and comfort that it offers. So there are pluses and minuses here.