I dislike it a lot. I tend to want to keep them forever too, and I always feel like a failure when critters turn out to not be compatible with each other. Thankfully this hasn't come up often for me, since I make a point to ask in a relevant subforum before springing on a new purchase. Re: labor and reduced time available due to pregnancy and childrearing: If setting your home up to automate waterchanges is at all feasible, there are TONS of great articles on here in the Setup and DIY section dedicated to making your fishkeeping life easier. I plan on having my cake and eating it when the time comes!
Oh, and re: tanks themselves: What is your stock like? Would the fish going into the 20 and 29 be compatible with each other? Having one 55 with the filtration from both 55s might be a more stable (read: lower maintenance) option compared to the separate 20 and 29s. Best of luck to you, and I'm glad you are keeping some animals, a home with no creatures is no home at all.