Looks like the makings of an epic road trip!
check out: MotorValley Emilia Romagna | Sito ufficiale dei Motori in Emilia Romagna
for motor related activities in Italy. << Great site!! >>
I've listed some thoughts / recommendations from my experiences along your provisional route:
<< Anfanuts >>
Drive the Col du Grand Ballon, on the way to Mulhouse.
<< Near where we are staying for a few days. Added POI.>>
Visit Cité de l'Automobile (the Schlumpf Collection) in Mulhouse.
<< Passing by, added POI. >>
Bern to Montreux: via Spiez -> Juanpass -> Bulle.
<< From Zermatt - Complicated. Open?? Or via Lotscberg train/tunnel, or back up Rhone valley and take Grimmelpass?? >>
Obergoms to Realp: via the Furka Pass (not the Furka-Basistunnel).
<< Done long ago but will do again now but maybe Simplon as half as long/time. >>
Milan = Alfa Museum (obviously) and the Mille Miglia Museum in Brescia.
<< On the plan, closed last trip. Stay in Rho? >>
Bologna = Ferruccio Lamborghini Museum. (museolamborghini.com) or Ducati Museum?
<< Modena Ferrri, Maserati and Lambo. Booked in Modena for Ferari.>>
Stop in Spezia, take a train to Vernazza (Cinque Terre).
<<Did the coastal boat tour and visited Vernazza, but will do some train and hiking this time out of Santa Margherita. Al so already hit Pisa and Florence for a week. Staying near Lucca in Montecello for 4 nights.>>
Detour from Menton to Sospel and drive the Col de Turini.
<< Noted as POI. >>
Avoid Saint Tropez (its a nice place but traffic is a nightmare)
Between Nice & Orange - Detour through the Parc naturel régional du Verdon and over Mt Ventoux.
<<In-laws lived in Viens, did this whole area extensively over many trips.>>
Paris = side trip to Versailles?
<<Been to Paris many, may times, even lived there for a while on work, Versailles a half dozen times.>>
St Malo = visit Mont Saint-Michel
<<Been 3 times. Focus on WWII sites.>>
Caen = impressive WWII Museum and side trip to Arromanches-les-Bains? (Mulberry Harbour)
<< We plan on hitting WWII sites on the coast hugging D-routes, so yes. Added POI.>>
Stop in Hon Fleur (near Le Harve)
<< Added POI. Looks cute. Staying at Le Tourqay.>>
Calais to Bruges - Detour via Ypres (Menin Gate)
<< Noted POI but taking northern route so may be out of way.>>
Between Antwerp & Lier - visit Guy Moerenhout's Abarth Museum?
<< Dito above. out of way. Maybe while in Lommel??>>