One question...
Has anyone ended up with a party where all 4 has entered through Duty Roulette? Or has it always been at least one person that have queued up through the Duty Finder (level can't tell you this)? (I can imagine that the Duty Roulette starts matching together parties from Duty Roulette only, if there is nothing to fill up in the Duty Finder queue, but have yet to see this happen myself)
A high level may queue up with the duty finder for low level dungeons in order to get gear for their alt classes...

(Myself I've only gotten Tam-Tara, Copperbell and baby Ifrit so far from the low level duty roulette)