It would be very interesting if pollsters asked which party people would ideally want to see in power, as well as which one they would actually vote for (the second question being influenced by tactical considerations in the respondent's consituency).
Yes I think it would be interesting also. I do also think it would be hard to extrapolate into
actual predictions though, as a lot of people don't really know how the current voting system works, let alone proposed systems. In fact when the AV referendum came around it was one of my first votes, and frankly I didn't understand it.
I run a polling station for elections and the number of people who come in and ask who the "X" candidate is, and we have to be impartial so we just direct them to the list of candidates, then they kick off because nobody from "X" is standing, or they can't find person "Y" on the ballot paper (when person "Y" is the party leader, not the local candidate), suggests to me that a lot of voters wouldn't
immediately recognise different voting systems (though I'm sure they'd understand it after a brief explanation).
They could have said the same on many other issues, explaining that the constraints of being in a coalition made their influence very limited. And the way Clegg looked so smug about being in power didn't do them much good either. They were also shafted by Osborne on things such as the electoral reform referendum, which was scheduled at the height of the party's midterm unpopularity, and on other things too. That came back to bite him (and the rest of us) when Cameron committed to the Brexit referendum in the likely expectation that he wouldn't win outright and he'd "have" to cancel it as a condition of LibDem support.
If they go too hard on social care they run the risk of it being another tuition fee issue for them in a future election - an expensive policy they are very publicly committed too, and they find themselves a junior partner in a coalition where the other party is unwilling or unable to concede it.
The difference being, for the tuition fee vote it was explicitly negotiated the ability to abstain in the coalition agreement. On the other major topics either the coalition agreement forced a vote in a particular way, at which point your party line to the public is, "We had to vote this way because we're a minority party in a coalition, and we had to make compromises." On tuition fees, they spent months saying we'll vote against raising tuition fees, negotiated abstaining on the raising tuition fee vote in the coalition agreement, then vote for raising tuition fees. I was working in a students' union at the time, and we saw our internal support for Lib Dems drop off a cliff.