Would you be happier to take on a job if...

#1 For me yes.
but it is pretty hard to get content that solid.

but even if the primary draft content is acceptable and usable, it would be a great headstart to getting it done.

for example, here at work that is how I have it done.
Everything is presented to me in a final draft, a design doc and the corresponding content.
I assemble it all and report any issues that need to be refactored or whatever.

it is a good way to accelerate development, as long as the content is solid enough.

#2 I reckon the only thing that makes a project appealing is the chance to develop something new and interesting


ps you describe an impossibe scenario above, the only place such a project can exist is on paper

#3 Id do it

#4 It's nice to work with final art. But, the team needs to be flexible enough to refine art and gameplay based on playtesting. I prefer to use rough art or sketches because the look is in place early and once the game is stable and refined, the artist can spend their time to put together final art. I've seen an artist redo assets a half-dozen times as minor things have changed. The artist was happier when they could put together a new set of sketches in half-a-day and then clean art only at the end of the project.

#5 It doesn't make it more appealing to me, what does is the commitment to actually getting the game produced with a solid plan. No project ends up the exact way it was intended from the outset so there needs to be flexibility built in to adjust any part during the development and testing stages.

Personally I prefer to get some base artwork to get a prototype up and running a quickly as possible, that way new ideas, art, functionality can actually be visualized and played around with - a great morale boost for the team to see them working.