Namecoin is definitely undervalued.

Pros:

• Firstly, there are only 21*10^6 coins, that is the supply is limited, and most of the coins are already mined.
• Secondly, it is very secure due to merged mining in combination with Bitcoin.
• Thirdly, it is more than a simple coin, since it also represents an independent naming system.
• Fourthly, it is the first altcoin.

Compare Namecoin with Litecoin. Litecoin has four times the supply of Namecoin and was introduced after Namecoin. However, one LTC is roughly 50 times more valuable, than one NMC. In the moment, Namecoin is cheap as dirt!

Cons:

There is one whale, who owns more than 10% of all Namecoins:

https://bitinfocharts.com/top-100-richest-namecoin-addresses.html
https://bitinfocharts.com/namecoin/address/MxvgLoWZYuvbdQqroXz8C82oW2cszmkhUw