Actually, I think the current accepted name on pierardii/aphyllum is Den. cucullatum, but who can keep track?

Most people still seem to know it as pierardii.
It's not necessary or always even advisable to keep these bone-dry in the winter, in their natural habitat they do tend to receive some moisture from heavy dews in the morning for at least part of the winter. The single most important blooming cue for the 'nobile-type' Dens is cooler temperatures, though all the ones I grow need far less water in cool weather (particularly after they lose their leaves) than they do during active growth.
Keikis seem to occur more often when a plant is over-fertilized (too much nitrogen) or stressed in some way, such as root or rhizome damage. Over-drying to the point where the pseudobulbs get all shrivelly is probably not a good idea for this reason. Overwatering is a factor in that plants not using excess water are more likely to get root rot, particularly in cool weather. Certain species like cucullatum (pierardii) and loddigesii will almost always 'keiki' no matter how you grow them, it's just their natural growth habit to branch and vine like that. Good luck, you picked some gorgeous Dendrobiums to start with!
--Nat