Interesting... If a little convoluted. The problem I foresee is that some variants of "rules lawyer" do it because tinkering with the minutiae of the rules or arguing to gain an advantage are what they enjoy, much like one player enjoys the tactics and excitement of combat and another likes the characterization and dialogue of role-playing. While consistency is important, if something like this crops up too often, it creates the danger of slowing things down to the detriment of everyone who doesn't find the particulars of half-monster prestige multi-classing the subject of fascination.
At the risk of sounding flippant, sometimes there's more virtue to just "winging it", a skill that every GM should learn. There will absolutely be times when a serious and/or recurring problem demands this kind of deep analysis, and certainly a GM should appear to be fair and consistant for the long-term health of the campaign. But there are other times when it would be well to just make a ruling and move on.
The particular problem raises different questions to me as a GM; I think I would possibly come to a similar conclusion, but for different reasons. The peculiarities of "levitate" (a second level spell) are clearly in place to differentiate it and weaken it in comparison to "fly" (a third level spell, and one which allows movement in all directions.) It's hard to imagine a case where a magician with access to and need for "fly" would put "levitate" on the same spell list. The letter of the law is that this spell is to be used for horizontal movement, and this spell is not, excepting the ceiling rule to prevent it from lacking the most basic functionality. Conversely, though, the players' "flycycle" idea is a rather novel way of using two spells to overcome the inherent limitation of "levitate", and such innovation should be rewarded (not least because it encourages such lateral thinking and makes the game more enjoyable for everyone involved.) A brief look over the two spells might suggest that the thusly-created "flycycle" could work for, say, floating across a pit, but would certainly lack the agility of someone casting "fly". And the caster of the disk might have to keep a constant concentration on the act of keeping the disk where he or she wanted it (with the pole), as the disk will try to keep returning to 6' from the caster whether he or she wants it to or not. Likewise, the character on the disk might require similar concentration to keep "on balance" on the invisible platform enabling his or her horizontal momentum. I wouldn't advise taking such an arrangement into combat.