On the Etrex30x these are stored on the SD card, so this not really a problem. The only capacity limitation is for registered tracks as these are stored in the internal memory. But I never got to a limit, even on a 2000km bike tour with a trackpoint every second.
However, I confirm all the other points. The only reason to choose an other kind of device would be better GPS precision. My Etrex is always some meters away from what I see on the aerial images. And this gets worse under certain conditions. It is ok for navigation and for documenting the trips but for mapping things not visible on the imagery, more precision would be really nice.
The small screen is another downside. It is ok for navigation but nearly unusable for orientation or looking up something on the map.