As I understand it, the "rub-off" is only really noticeable on albinos and other really light colored snakes. It's not harmful though and doesn't always happen.
I use the unprinted paper that you get from moving. The military moves us, so I have TONS of the stuff. (I mean TONS...) I just use one sheet per tub, folded in half, so there are two layers. Works great for absorbing wastes and spilled water.
I don't bother changing for spilled water (my bowls aren't big enough to completely flood the tub), but I do change it anytime I notice bio waste. It's really quick and easy. Slip the snake into an empty bin or bag...pull out water bowl and hide...pull out paper..wipe down tub with sanitary wipe and dry...toss in a new sheet....replace items and animal. SSOOO much easier than aspen or anything shredded.
And yeah...aspen may absorb more urine...but personally, I wouldn't be able to stand the idea of them laying in their own pee, no matter what. It's just gross. So the type of substrate would not change my frequency of cleaning...just changes how quick & easy that cleaning is.
And I agree....don't mess with the repti-carpet stuff. Worse than worthless.