IMHO you are forgetting about the opportunity costs associated with having your money tied up in these hobbies. How much over your life time could you have made, but having that money invested?
Also there is additional lost costs with the hobbies you mentioned.
Motorcycle (i have an 07 cbr 600 that i raced for a few years before i started on the path to FI, its for sale now)- Protective Equipment, Registration, Insurance, gas for those days where you just went joy riding, maintenance (oil, tires any thing else it may have needed)
Aquarium - there is a huge cost associated with filtering, lighting, the plants and fish you are going to keep in it, food for the fish
Indoor trainer - the cost of time, go ride your bike outside, take care of some errands, get fresh air, socialize with other riders. But good for you if you sell it at a large profit, not so sure I would categorize this as a hobby either, if you are planning to hold it for such a short period of time and just flip it.
I have a lot of friends who try to justify their spending in the same way, but they don't think about all the associated cost that go along with owning these toys. And what if you cracked the aquarium, or dropped the CBR.
Just me 2 cents. Not knocking you for having some things that you enjoy, you just need to evaluate the entire picture and if all of the costs and if the hobby worth it, not just the purchase and selling price of the main piece of the puzzle. As you said though, you are in a better position then your friend who buy simular things brand new at full price from the store.