I have lots of free time and am on most of the time, yet with farming gold for the soul pyre mount don't have time for alts. I could use my alts more but it just requires effort that I don't have as it's all put towards my main, but once we get the soul pyre stallion I'm going to focus on levelling my alts as the extra star seed exchanges can be useful and as someone else said, they're useful for extra storage.
I've got a few alts I don't really play. Just leveled them until they had their estates, so I can do multiple full star seed exchanges and also pool together all of the estate build resources for faster progress. I think it was worth the effort