So which concept are you preferring?
I can see that its nice to have some portable gear, I don't consider my main case Portable cos its Blooming heavy but I'm working towards having a my Top Case and Percussion Case as being portable and easy to combine with a Beatstep Pro. This leaves my Main Case to be more Generative and experimental.
I want to develop another case that will be more about weird shit and sound mangling from external sources like Pizo pickups etc.
Enjoy your spare HP, don't rush to fill every last space, this is not like filling sticker books. Resist the urge to 'complete' your rack, its never complete so just relax.