Thank you all for your advice and thoughts.
So, after TiAm started a thread about the performance gains of making an object dormant instead of destroying it, I adjusted my earlier demo so that it no longer creates any sprites during run time. And, for my eyes at least, after destroying a few objects as j0schi suggested (thank you x 1000 for that great advice!!), the 'game' now runs very smoothly right from the start....
While tinkering around with the settings, I found that the performance improved only if the objects that are to be destroyed are created inside the layout (I initially set them to be created at -200, -200 and that had no effect on the first 10 seconds of garbage collection; it was smooth thereafter, however).
So, create and then destroy some stuff inside the layout and then don't create/destroy sprites during run time.... What about particles? I don't think they cause any stuttering. I'll try and put together another example to see if there are any limits / gains worthy of note.