Odd how you write it off with that parenthetical -- as though nobody has ubiquitous data connectivity? (Hint: I do.) So maybe I'm in denial, or maybe I validly find it works great, because I'm working under a different set of constraints.
How it is good for hiking: It lets you use Google, Microsoft, or Yahoo satellite maps. Does that advantage come with a price, in connectivity or storage? Sure. But I don't know of any other options to use satellite maps without either a live connection or downloading them all in advance, so it seems as good as any option.

And again, why is there the assumption that nobody could have a data connection? Some places are remote enough to not get a signal, but many places are covered adequately to make this a net advantage even without significant local storage. I download maps over wifi, but have twice been caught in places I had no maps for; downloading maps over EDGE is unpleasant, but not unworkable, at vehicle speeds, and as it needs maps proportionately less often at hiking speeds, I don't think it would be an issue.

The world is only getting more covered with data uplinks, so arguments that assume requiring one is a problem in its own right don't work well for me; it's only an issue for the few people who can't/won't afford a mobile with data, or the few places where even GPRS is unavailable. (Or, technically, one can use circuit-switched data out to GSM-only areas, but I'm not sure that it's worth the hassle and cost.)

And unless you were trying to download insanely large areas at fine zoom levels, I'm not sure where gobs of GB comes in. Just to check, I fired up MM and asked for a state-sized chunk (a screenful at level 13) of level 6 maps. Just under one GB estimated, and the estimates are generally long. From the looks of things, you could fit the entire US at level 8, a state at level 6, and smaller regions (where you actually plan to go) down to level 2, all on a 16GB card. (Not sure I'd want to wait for the download, though! )