On weekends, however, I let it run from Friday evening till Monday morn to let it do its maintenance thing in the wee hours. I note that on Monday evening's boot up it's noticeably snappier.
And your car runs better after you wash it!
I respectfully submit what you notice is in your head.
Amazing how long it takes old habits or legends to die...
BTW, you're certainly not alone in still worrying about the scripts but it is one less thing to think about while enjoying your Mac
Since Tiger the maintenance scripts are handled by the OS without you having to run them manually. And, even if you don't run them you will probably not notice a difference in the running of your Mac.
If you want to assure yourself that they are being run at a decent interval (remember they were originally designed for a server running 24/7) then you can check them in your console log or, better yet, use the widget done by our own GiantMike as a result of us discussing this a couple of years ago.
Don't bother leaving your Mac on over the weekends and risking the bad power hits unless you want to for other reasons.
FWIW, I haven't manually run the scripts in a couple of years and here's the current status as displayed by Mike's widget.