Quiltergal, yes you should start watering or at least heavy misting when buds appear. Like you, I have also lost buds on this and other orchids when in bud and I feel it is due to insufficient water or humidity so when I see buds appearing I provide a little more water or misting in the case of mounted plants.
Some people in my orchid society grow Den. aggregatum year around with regular culture and are successful with flowering.
Excluding Nobile types that can be pretty exact in their demands, I find that a lot of the dendrobiums take their long winter nap when they are ready and you can't wake them up until they are ready no matter how much water and fertilizer you give them. I have Den. parishii hanging beside Den. perinii . Perinii is blooming right now so it gets daily water since it is outside in dry windy conditions. Parishii gets water also. It's hanging there completely void of leaves but refuses to do anything until it's turn comes which will be in late May or early June.
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my blooms lasted a little over a week and have now died I have mine mounted too and also water daily since it is hot and the salt air can dry them out. Do I cut the spike off now??
Today when I was watering I discovered about ten spikes on my Den. Jenkensii. Normally I only get a couple of flowers but I am looking at the possibility of thirty or more if they don't blast.