I'm currently at the phase where I'm "trying" not to purchase one-off figures.
Unfortunately, I've got a large number of those "one-off" figures, mostly in the Sci-Fi genre. Added to the mix are custom built figures that fall anywhere in any of those lines.
I do the same - and my new strategy is the following for non-main themes or because you can't show them all off at once anyway:
I try to figure out either the most famous 2-3 characters or my personal favourite 2-3 characters from a certain genre/movie/game etc. and place them together on a shelf.
-> I love Game of Thrones, but I still only got Jon Snow and Daenerys and a 1/6 Iron Throne.
-> I also just preordered the Mandalorian and will shelf him together with Baby Yoda once available. And if season 2 brings us more famous chars, I will get one more
-> For Lord of the Rings I have Gandalf and Aragorn, would get Sauron if there is one. Thats it. Atm Saruman is in his place
I think having groups of 2-3 Figures is much better than one offs you like or trying to max out every theme (because of money and space).
If I will ever buy an Indiana Jones I would probably place him together with a Terminator and a Jack Sparrow as "famous movie figures"
In this last example you can also see the downside of my strategy: Instead of buying one figure, you buy three
haha