Arriving in Venice June 5 - staying at Hotel Danieli for 2 nights - we were considering moving over to the Westin Venice Lido for 1 night before heading to Tuscany via rental car. Is the transfer from Venice proper to Lido expensive and do you think the move is worth it?

I can't think of a good reason to move to the Lido. It is away from everything you would go to Venice for. I doubt that the transfer is expensive. Just take a vaporetto (unless you are travelling with a pile of luggage.

The transfer isn't expensive, but I would extend your stay at the Danieli rather than moving over to the Lido. When we stayed on the Lido a few years ago, the water looked and felt polluted.

I went to Venice last year and went to the Lido one Sunday late in the afternoon. It was a big disappointment. I felt like I had gone to a totally different place in Italy. It's got nothing to do with Venice. It's an ordinary beach with ordinary shops and restaurants. I'd stay the entire time in Venice and spend an afternoon there. That'd be more than enough. It's ten minutes away from Venice on vaporetto. I don't remember the price, but the vaporetto is really cheap and they operate 24 hours from Monday to Sunday (that's what one of the members of the vaporetto crew told me), so you can stay there as late as you want. I'm not advising you not to go, but to keep in mind that the Lido doesn't have that idyllic charm of "Death in Venice" or "La Dolce Vita" of past times. It's just my opinion.

I don't see any point in moving to the Lido to stay there for just one night. You don't have a lot of time as it is so don't waste a few hours of one day packing up, transferring and checking in somewhere else.

If you really want to see the Lido then just get a vaporetto there one day. With such little time, the Lido probably wouldn't feature on my "to do" list.

When we visited Venice we stayed on the Lido for four nights and we loved it. The vaporetto takes 12 minutes from the Lido to San Marco - this means you are quicker there than from many Hotels in Venice. You pay the usual fare. I understand that the Westin has a hotel boat that will bring you even faster to town.
Staying on the Lido is a different experience. It is quiet and green and you have this long sandy beach.
When we stayed there we went to Venice not before 3 p.m. - after most of the tourist buses have left.

The Lido is not what makes Venice Venice. It has a couple of luxury hotels with private beaches (OK), a public beach (not vey nice), modern Convention Center, etc - and if there is a convention on there can be long lines for the boat to get back to St, Mark's (up to 45 minutes on line plus the boat ride).

I do no reco this. Stay in the Danieli - much closer to everything you want to see/do.

Don't even think about it! Don't even bother with the Lido - its got nasty noisy cars!! There is so much to enjoy in Venice - with limited time go up the Campanile in the late afternoon, go to Burano (boats take about 40 mins from Fondamenta Nuove), have a Prosecco
inside Florians, take the vaporetto up and down the Grand Canal - at night if you can. When you arrive at airport you can buy a 3/4 day ticket that covers all the boats so you can just hop on and off. (you have to stamp it in the yellow machine at the boat stop to start it off.) Don't bother with Doges Palace - its so big it will just tire you out! I could go on & on...

The price for the vaporetto ride to the Lido is 3,50 Euros per person, and as another poster has already pointed out, it's a matter of a few minutes to arrive.
If you want to see the Lido, you can just hop over while being in Venice, but it would be crazy to move to the Lido for your last night - not just because it's so near to Venice, but also because the Lido is by far the ugliest part of Venice. The only reason to go there is the boat ride back to town, which rewards you for the ugly experience of having seen the Lido with the very best view on San Marco.

With only a couple of days in Venice, you'll be hard put to see what historic Venice has to offer, let alone head to a beach resort.

The Lido of Venice would be very, very low on my priority list for a visit to the most unique of Europe's cities.