Hmmm, well to add my bit one aspect of Venice that doesn't seem to be mentioned is its market structure. Specially that
- It is focused on luxuriant
- The lack of an internal market
- The state mostly derives revenue from trade
- The high standard of living
- The large amount of state control
The Venetian problem with luxuriant manufacturing is that it is relative labour intensive and hard to mechanize. This also ties in nicely with the next point:
The lack of a large internal market which skews the focus away from bulk industrial goods to harder to mechanize higher margin luxuriant goods. Not overwhelming but still a factor.
The high standard of living, which increased labour costs that increased the incentives for mechanization: but in the Venetian case it also made them less competitive. A good detailed examination of the specific industries can be found in "Moderata Fonte: Women and Life in Sixteenth-Century Venice" which offers a first hand look at the particular industries in Venice at the time.
The last one is probably the biggest, due to the lack of a hinterland the Venetian state derived most of its revenue from taxes on exports and imports severely reducing Venetian competitiveness. Furthermore the sheer amount of state "quality" bureaus stifled innovation and forced an absurd focus on quality above all else retarding the market of lower quality industrial goods.
(unfortunately these are from the personal notes of Professor J. Cuenca From Waterloo university, not exactly a public resource)
As for the Portuguese competition it was relatively insignificant: