I'm sure plenty of guys do, and probably people like KK Downing and Glenn Tipton - have a listen to the sweeps they do on Painkiller (and some limited stuff they did as far back as Turbo), it's not your usual 'guitar shred hero' type sweeping. At the end of the day, sweeping as such is just an effect - what notes you hit it entirely up to you, be it arpeggios or you're doing "economy picking" across a scale like Frank Gambale does, etc. If you don't want to play root-3-5 style arpeggios over anything, don't! What I would recommend though is to work out if those "random" power chords are based on any particular scale, though, so you're able to apply a little more knowledge behind what you put over it. At the end of the day, you might find you're modulating from scale to scale even in the middle of a bar, but if you can find a pattern of chords that repeats and can work out the scale that's most appropriate to fit over that part of the progression, you'll know better what to fit over the top. And of course, on the other hand, sometimes going "fuck this, you know what sounds good over this? This here dive bomb and chromatic based noodling" where the scale is almost irrelevant - it's the attitude and the intent of the scale rather than a specific theoretical purpose to it. I guess what I'm saying here is that if you're worried about working stuff out a lot, work out the chords and apply the theory. If not, don't worry about it. If it sounds good/appropriate, it IS good and that goes for any shapes you may want to use for a sweep idea too.