Help with Vaporetto?

If it were me, I would buy a pass for the entire time I was in Venice. It is a like a bus, taking you many places around the city. Yes, Venice is small and very walkable but we like the freedom of having the pass.
We loved staying in Cannaregio where we had an apartment for two weeks on our third trip to Venice. It was our favourite area we have stayed in.

Here is a schematic of all the vaporetto lines.
http://actv.avmspa.it/sites/default/files/attachments/MAP%20OF%20THE%20SERVICES%20ACTV.pdf

If you have a smartphone with data service, there's an app for that.
http://actv.avmspa.it/en/content/avm-venezia-official-app

Check out eurpoeforvisitors.com/venice, great resource for Venice

Get a multi day pass for your stay.
The vaporetto comes in real handy, you'll end up wishing you had that pass rather than pay for individual rides.

A Vaporetto Pass is one of the few bargains in Venice. And there are so many ways to use it besides getting someplace. Early in the morning, take it to watch Venice wake up - it's a very different city then! In the afternoon take it to get back to your apartment for a much needed rest (sure beats walking if you're really far from the apartment!). At dusk, cruise the Grand Canal and watch the night life begin, when Venice is even more magical. Then right before bedtime, take it again to help you relax and ease your way into a great night's sleep. And I've only just gotten started!

Is the Venezia Unica "frequent user" card a good value for tourists returning to Venice at least once per year?

yes, but remember that some trips will take you more than one discounted fare because unlike the unlimited usage with xx hours passes each ride is for a limited duration. Without checking I think it may be 75 minutes, and if you go out into the lagoon you will exceed that. You also have the hassle of dealing with the bureaucracy at the little office at P Roma, and then keeping track of how many tickets are on each card (one per person, non transferable with photo) and reloading it, but all in all if you use it frequently and often it is a real money saver.

That's quite a leap of faith for a first time visitor.

I return to Venice frequently and have one.

Just found this site. Thought it may be helpful to others who are also not familiar with using the Vaporettos in Venice.
They offer a map of all the individual trips/Line Numbers, the direction of operation, and a list of all the related stops.
Found this very helpful.
https://www.visit-venice-italy.com/water-bus-venice-all-lines-maps-actv-alilaguna.html

If the website isn't maintained by ACTV the tables and graphics may be out of date. Any official ACTV like http://muoversi.venezia.it/en/content/moving-venice-1 will have up to date info.

Consider an app - the best isn't mentioned by ACTV - but excellent anyway, and with up to the minute information - CheBateo is used by most locals and me. It will tell you just when and where to get your boat.

You'll want to think particularly of places you can't get to on foot, but can by vaporetto - islands of the lagoon (Murano, Burano, Torcello, etc.), San Giorgio Maggiore...

Great advice!! I also have a question about the vaporettos. I would like to get an idea of how long they take to get to places so I can better plan our outings and tours. If we have a tour (Secret Itineraries) at 9:55am, at what time should we be at in the Santa Lucia Train Station area to get onto a vaporetto and be on time for our tour? Do the apps mentioned mention times and durations? We are also meeting at Campo Santo Stefano at 10am on another day (also departing from santa lucia train station area). Any advice would be appreciated!

I suppose they do, but you can also look up the time tables for each vaporetto line.
http://actv.avmspa.it/en/content/orari-servizio-di-navigazione-0