I guess there is no definitive "right answer" for this as everyone's motives are different and also have the tendency to evolve with time.
The best advice thus that I can give is the same I was given when faced with the same dilemma:
"choose what you like".
This I have found to be true with a long passion of mine - wristwatches - and thus it was somewhat easy for me to accept this advice when it was given to me by a highly regarded senior keris student. - Ultimately we can rationalize all kinds of "rules of engagement" what comes to forming a collection but non will be of much use unless you enjoy what you have.
Someone else´s mileage may vary and to prove that I drive in kilometers - not miles
Enjoy the hunt!