well the most devaluated alt coin its in my opinion doge it should be to 300 satoshis a piece cause its going to still rise its difficulty
You must hold a lot of Doge like me.
Honestly, I think Doge is over valued due to it bieing over hyped. But I would like to see it go to 300 as you say so I can sell at a small profit.
Difficulty does not determine price, but price determines difficulty.
Doge's real value is perhaps 0.00000012 LTC (not BTC)
nxt is pretty darn undervalued atm 
I can't really say much for NXT. Haven't spent the time to deeply study it and honestly (from what I know so far) too complicated to be successful in my opinion. I see a lot of noise surrounding it, but I for some reason just don't find NXT interesting. I do like however that it's implemented in Java.
But yeah, considering all the noise around NXT I was surprised to see how inexpensive it was.
As for the most undervalued: well Zetacoin of course. I say that not because I hold ZET (I don't have any more than a few hundred), but because of it's economic factors, age, and technical background.
Zetacoin's lower end value should be at $5 per 1 ZET, and correct value at $10 per 1 ZET. However, I understand why it's currently valued at about $0.01 per 1 ZET. It's only been around 2 and a half years, gets very little attention, is often overlooked, and there are still many who probably have 100k+ ZET wallets. Once those large holders sell off, the value of ZET can start rising to it's correct level.