Looking to add and additional unit for mapping only. Are there any mapping differences (raster displays - etc) between Gen 1 and Gen 2 models?

Thanks.

The main differences between Gen 1 and Gen 2 are processor and internal memory. Gen 1 will display some colours slightly different then Gen 2 but not much. (I have both side by side so I see the difference.) If you want to map large lakes using raster, Gen 2 redraws a lot faster when zooming in and out. It does so with large vector-maps as well, but raster really kills the Gen 1 if it's a big map. With HDS Gen 2 looking like it will be discontinued for 2015, you should be able to get one at a good price. The Touch-models continue in 2015.

The Gen1 also cannot display any newer features (e. g. INFOBOX for lines and areas) or features from the next future IMC release (e. g. hexadecimal colors). But this differences are only important if You want to use really all chart options.