Even if you have Bose speakers, you will hear better sound from a better cartridge.
This is true, I think. One seriously interesting way to spend a budget is to put 80% of it into the source, then upgrade downstream as savings permit.
So I agree it might make some sense to listen to a great cartridge with Brand X speakers, if you hoped to upgrade eventually. The upgrade would only let you hear more of what the cartridge was already doing (but inaudibly) with those Brand X speakers. You have the highest-resolution component upstream. All systems should be balanced like this.
That's why it doesn't make sense to use a premium cartridge with an entry-level arm (and/or turntable). To put it one way, the cartridge's great resolution would let you hear the arm's limits much more clearly. Put another way, you would not be getting the best performance for the money you spent on the cartridge; whereas if you spent the money on upgrading the arm, you would then be getting more out of the cart.