Good tracks are good tracks no matter the origin and all of the PD original courses are good-to-great tracks and the best of these rival the best of what you could drive in the real world. Just as I can enjoy driving Spa and Suzuka for the next 30+ years, I can also enjoy driving Trial Mountain and Grand Valley for just as long. I see absolutely no reason to get rid of circuits that are not just considered classics in regard to the GT series, but are simply great circuits to drive. PD will have many unhappy customers if they abandon what has been so good for them.
I'd even race Rome-Night (GT2) than the GT5 Rome Circuit. Rome-Night is what I've called the most under-utilized racing course in GT history. Perfectly fine course that is somehow so sacred since no real races take on this course.
The problem with Rome-Night is that it is the only circuit with a name that references a real location but takes place in a completely fictional environment. It is also the only street circuit since GT1, bar SSR7, (and isn't an updated version of a GT1 track) that is located in a fictional environment. All other non-GT1 street circuits (Seattle, both "day" Romes, Tokyo, Seoul, Hong Kong, New York, Madrid, etc.) occur in actual or slightly modified real world locations (or in the case of Eiger, Citta and Costa, heavily modified locations). If Rome-Night came back, I would imagine it would need a name update to match it's fantasy location and fall in line with the other complete GT fantasy street circuits (SSR5, CSR5, SSR11, SSR7). Something like Historic City Route 4, HCR4, could work.
But I agree with your post, I'd like to see many of the old original GT tracks come back, updated perhaps in terms of "safety" where possible, but without changing the character.