is the winning bid on this ever not 3?
Why would the winning bid be 3? That seems like a bad consolation pirze for not being able to do anything on the first shuffle.
I think a bid of 3VP would always win the auction, but would not be a good value proposition.
I think there are certainly boards on which it is optimal for no player to bid on Valley Retreat at all.
I think that's possible, although I'm not entirely convinced. Holger suggested it might not be worth bidding in "a kingdom with a strong pin or golden deck strategy. Or in one of those puzzle solutions "win the game in 1 turn"...

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In theory, if you're going to get completely pinned, then it might not be worth 40VP, although I'm not sure how that would work.
With a strong golden deck strategy the best case scenario (as far as I can tell, absent something extremely elaborate) is that you can buy a Colony each turn after Exiling the one your previously bought (Platinum - Gold - Gold - Sanctuary - Colony), probably set up with Donate and maybe Treasure Map. In that case, the player who wins the bidding could still go after that golden deck, they would just be two turns behind. In a 2 player game that would result in a 3/5 Colony split, which would only be a 20 VP advantage. Even if you split 6/2, a 40VP bid would tie the game.
If someone is going to end the game on turn 1, then this might be the only way to for the other players to get any VP[?!?].
The bigger issue with this is that it will just feel terrible to win this. Even if it's worth the VP that you get, you will play the whole game feeling like you're behind and being able to do less than the other players. I'm not convinced that it's a fun gameplay experience.
I guess it could feel this way in a Kingdom with really a great engine, that you would miss out on, but otherwise I think it would feel like you are starting out ahead, and the other player(s) are trying to catch up. To look at it another way, you are doing less, but you have less you have to do to win.
One of the things I kind of like about this is it makes it so the players aren't playing exactly the same game. Those who don't win the auction have to figure out a way to make up for the deficit, while the player who did win needs to figure out how to keep the head start while playing with a weaker deck. There is a gameplay element that can sometimes be missing from Dominion.
My concern would be that it doesn't make sense not to open the bidding at 40VP, so you could end up going through many bidding rounds and the end result could be very underwhelming. I'm not sure it's worth making the game longer.
I do think 40VP is usually (if not always) the opening bid, which may be quickly followed by 39, 38, etc., but at some point the players will have to decide how low they are are actually willing to go, which they would have to spend some time thinking about, which they would do at the same time (and as part of) thinking about what strategy they want to use given the Kingdom. I think that would add a little time at the beginning, but I don't think there would necessarily be long, drawn out bidding sessions (but I could be wrong).
Thinking about this, it occurred to me that you could actually test this card out on Shuffle iT, bidding in the chat box, having the winner forego buying anything to pay down the (imaginary) debt, then adding the (not game recognized) VP won to the official score at the end of the game.