What is the basis for the difference of opinion whether the extra Dinar should be a Dinar of real estate? could it be that those who say it must be real estate are of the opinion that we wish the inheritance of the Yorshim to be "Nahala", which is land, and the opposite point of view is that we are not concerned with "Nahala" at all, only with "Yerusha", which need not be land?
The second point is whether the land should be free of any lien. Do we really know about liens when the inheritors come to distribute the estate? What will happen if after a few years a person comes with a good bill, showing the the father owed him a large sum of money which he never collected, (and with a Pruzbul) and which he now wishes to collect, and now it transpires that the extra Dinar actually had a lien on it? Will we cancel everything done by the courts in deciding who gets what of the inheritance, and divide from the beginning? Or is this Din only a sort of "Lechathila"? Does this have anything to do with the issue of "Im Ken - Ma Koah Bet Din Yafe"?
As for your second question, whenever an old creditor will come, we will have to redistribute the Yerushah. This is no more characteristic of Kesuvas Benin Dichrin than any other Yerushah. Of course, this Din is not merely a l'Chatchilah. The question is if we relate to property inherited with a Shi'abud on it as a Kiyum of Yerushah d'Oraisa, or since it is actually owed to the creditor it is as if it was not inherited at all.
As for your first point, the question whether we need real estate in order for there to be a Yerushah d'Oraisa is probably due to the fact that since Kesuvah is not collected from other assets, and so too Kesuvas Benin Dichrin, the entire question of the Kesuvas Benin Dichrin only relates to real estate and therefore we may wish to favor Yerushah d'Oraisa over the Takanah d'Rabanan.
D.Z.