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The power ratings listed on PSUs are the MAXIMUM they can safely draw without melting. The mac mini in practice draws nowhere near that.
If you need to reboot, you're rebooting for a reason - likely because something in that "50 to 75 MB" has changed.
Of course, if your box doesn't support suspending to ram, then hibernation is an ok alternative. But sometimes hibernate can be just as slow, if not slower than rebooting.
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