Hit the nail on the head. Auctions tap in to emotion and competitiveness.
You might have in your mind a figure that you are prepared to pay but as the auction progresses you can easily justify to yourself amidst all the action that it is worth that 'little bit more' and hence overpay.
I think it can go either way personally. Their is emotional elements like you say, and I think also the "well this guy it bidding to 10k so it must be worth around that level" as a factor. Competition also as you say, the bidders focus on other bidders not the seller and want to "win". So all positive factors for the seller.
On the other hand sometimes you can have one really strong bidder in with other bidders which might result in worse outcome than a private sale (ie the guy is willing to overpay, being willing to pay way higher in a private sale than where it ended at auction). I personally like auctions but but several times I've sold names for less at auction than recent offers.
Also other issues like registering to bid. Had one recently where a couple of people had tried to buy a particular name before, one told me just before the end of the auction he couldn't be bothered with the registration process (can understand that because I probably wouldn't bother with it also unless I really had to have the name) and another said the auction house couldn't process his application in time.
The other issue can be if a name passes in well under reserves bidders tend to think it must be worth what it ended at, the flip side is some people won't bother bidding unless they think it will sell so the market has never really been seen for the name. You might have 7 bidding and another 3 others will to bid if it looks like it will sell.
Personally like auctions though as I think it best approximates where the market is most of the time.