A 4 tile range (probably for the capital only) would be a very interesting UA for another civ.
Venice is strong as is. I play King\Emperor (was Prince\King in G+K), but I won a Deity game as Venice on archipelago. If anything, their trade route bonus could be nerfed from double to 50% more, though I don't think that's necessary either.
I could write a lot about playing Venice, but my quick advice is:
- Use internal trade routes to give as many apples to Venice as you can.
- Build the market\bank\exchange in good time (without killing yourself over it) and always work the merchants.
- IMO Tradition is better than Liberty because of the apple routes, even though Liberty is very good for them.
- Don't be afraid to make Friendships for Research Agreements - make trade routes to every civ to decrease risk of denouncement\war over this.
- Buy CSs that are on the coast and have a lot of units. Leave a quarter to a third of them to ally if going for diplo victory - the Level 3 Freedom tenet that gives influence for trade routes is late-game dynamite for Venice.