Great thing to wonder about!
In the Lean Startup sense, the M is about minimum effort, and the V is about viability with customers. You're basically playing Battleship trying to discover where those two Venn circles overlap.
Different aspects of quality map to both those circles. There's build quality, which relates to the sustainability of the code base. There, you have to consider both short- and long-term quality. [1]
There's also quality as users perceive it. That varies widely by domain by market, and by how far you are along the adopter curve.
My general answer is the same as yours: minimal features with highly sustainable code. But for experiments, I think you can get away with terrible code as long as you a) throw it away quickly, and b) you are on it so even if you have a bad MTBF, your MTTR is really good.
I also think that you can tactically discard certain kinds of user-side quality. E.g., if I'm making a product for early-adopter financial traders, I'm not going to worry about quality of visual design, and I might inflict hard-to-learn interfaces on them. But I'd be rigorous about accounting and about UI issues that might lead to mistaken trades.
[1] I wrote some about that here: http://agilefocus.com/2009/06/22/the-3-kinds-of-code/