I think that is the exact opposite of what needs to happen, and I'm not sure where you see a consensus at all.
The Rialto District is the flexible one. It gives gold if there's anyone you aren't at war with, lets you spend gold easier, get more MoVs, and have votes (which are inherently flexible).
The Murano Glassworks is better the fewer cities you have, because it boosts the capital significantly more than it boosts any other city (you'll want to place your GP Improvements here, leaving your other cities bare).
The Arsenale di Venezia is supposed to be for military and conquering. +15% production isnt really any better than the -10% gold cost and is also pretty negligible overall, especially since one of Venice's strengths is buying units in all the puppets, bypassing and reducing the effectiveness of the Arsenale. The naval upgrade itself is good but not interesting.
There's many ways to improve the Arsenale, but just buffing it is probably not going to work. And trying to make it more flexible is probably not the way to go.
Flexible appeal = good for war, but also has lasting value while not at war.
G