Something like this is a cool idea for those who don't have their NES anymore and want to rekindle the flame of gaming past. Sure they could buy a NES from a thrift or eBay but that may not be their bag anymore. However if these people are into portable gaming they may already have a GBA or an SP and with the sheer millions of GBA and SPs that are owned who else would buy these that would make the release worth while? They aren't really priced to "buy one...buy three for your family!", even though Nintendo seems to think that's how people buy these systems.
While it's a trip to see the classics rereleased I too think $20 is a bit high, especially since Nintendo has devalued some of their classic games. Like it was mentioned earlier, you can get NES games in Animal Crossing (and can't you transfer them to your GBA?), some of the titles being released were already available for the eReader (granted they were limited a bit but still $.01 to $4 a pop plus the eReader is still cheaper for multiple games) and have been released in compilations (the Zelda compilation for example). On top of that we have the GBA rereleases of classic Mario games like Mario 2 and 3 with a SNES style graphical makeover. SMB and even Zelda is going to be a helluva shock for those who never played them "back in the day" and may be expecting them to look like the modernized versions of the franchises.
Personally, I too think Nintendo is re-heelly milking their past calatog. It's like at the peak of the Game Boy Color they decided to not make any new franchise games. The only new Mario game on the GBA is Superstar Saga. That's the first new true Mario game (true as in not a spin off like Golf or Tennis) on the GB platform since Super Mario Land 2, which was released in 1992 (SML 3 starred Wario so I'm not really counting that). If third party companies are making successful (actual) sequels/new titles to past franchises (the Mega Mans, the Castlevanias, etc.) why hasn't Nintendo jumped on? Get Capcom or even Sega to make a great Mario game. If done well it would be like printing money AND they wouldn't be alienating fans.