In my experience it's the constant on-offs that can lead to a problem, just like a light-bulb. In my previous job we had servers in Turkey running 5 years+ without a hitch (despite mountains of cigarette ash being dumped on them), until you went along to perform an upgrade and the thing would fail to reboot soon after you opened it up. I quickly learned to take a spare with me just in case...
So, IMHO opinion, with apologies to Mrs Bolt, the method you are following is better.
Though I would also add that the PSU, CPU fan and possibly the hard-disk are the weakest point in a PC due to the constant use of moving parts, which like the man in the shop said, don't last for ever when powered on/off all on a regular basis.
HTH