Well, since fingerprints can be layered and it's forensically possible to tell which fingerprints came first and last, yes, there could be a reason for any person staging a scene to wipe fingerprints.
If all of the fingerprints were on top of earlier fingerprints, it would show the last person to touch the bike. According to the alleged "Suzanne went biking" story, her fingerprints should be the last ones. Especially on areas like the brake levers.
Separating Overlapped Fingerprints - IEEE Journals & Magazine
It has occurred to me that Suzanne may not have ridden her bike recently. If it sat, unused, in the garage, then particles from the air (dust) would settle on top of the prints. That would be easily discernible. If Suzanne's prints were not recent/fresh, that would be discernible. We would expect her prints to be on the bike's saddle, on the grips, and on the brake levers. There might be little reason for her prints to appear on the forks or the frame of the bicycle, at least not recently.
Forensics would find her prints in these places and be able to tell how old or new they were (a bike would be a really good object on which prints could be preserved and then subject to particle fall-out from the air, especially if anyone ever started a car in the garage).
If, on top of those prints, smearing some of them, resided other prints and no new Suzanne prints on top of key places, that's a concern. It's an open/shut case maker, but it is certainly an important set of clues.
Similarly, if the found object of Suzanne's showed fingerprints on top of hers (two different people touching the phone, with the second person's pattern imprinted on top of the first one's) then that would be a reinforcing print pattern (someone other than Suzanne was the last person to touch those things).
Similarly, if prints were wiped, it seems likely someone other than Suzanne did that.
I would also assume that when the bike was taken into evidence, it was handled carefully (lifting it by its tires, perhaps, while wearing gloves).
I've been going with the "it was leaned up against a tree" idea even though that comes only from BM (and from BM to his nephew, etc).
The "in the ravine" theory...can't remember where that came from, does anyone remember?
Of course, LE could have bought the missing-on-bike ride theory and simply grabbed the bike by the bars and wheeled it into evidence, hopefully while gloved. That should still leave some evidence on other parts of the bike, especially if the bike wasn't ridden to the place where it was found.
Anyway, yes, there would be a reason for a family member to still wipe evidence, especially if the bike was going to show that Suzanne had not been riding recently.