"My name is Ozymandias, king of kings: / Look on my works, ye Mighty, and despair!"
Habeo in animo vivere in perpetuum aut mori dum conor.
In particular Brussels beascon, the Venetian fortress... and Malta
I can see the card reason for Rhodes but they are not even worth VPs...
They just get completely ignored in my games.
Brussels and Besancon can be useful for England or even France to take to eliminate the Hapsburg home space (because Charles V can teleport to a home space with his Home Card and start raising troops). It's not a high priority, but it definitely gets taken sometimes, particularly in the middle of a large conflict (and it's not usually well-defended).
I've never seen a Venetian fortress assaulted. I think those fortresses are mainly in the game to provide anti-piracy dice.
Malta is very rarely taken in HIS, but it can happen occasionally if Knights of St. John is played after Rhodes is captured and the Knights move into Malta. It also provides a valuable anti-piracy die.