The GBA SP improved the GBA design, but it still played the same games.
I had a GBA, never bought the SP, and never really felt cheated about it, especially since with the side-light (instead of a backlight), the SP was (in terms of the viewability of the screen, and only that aspect) the GBA with one of those third-party lighting devices built in.
If the 2nd analog is built into the next revision, I don't think that a reason to regret purchasing the original 3DS. Anyone here upset terribly about owning a Wiimote that doesn't include M+ inside? Anyone here feel wronged because they bought an N64 that didn't include the memory expansion? Anyone outraged because their NES bundle didn't include the NES Advantage Stick?
And if the only improvement in the next hardware revision is built in 2nd analog and extended battery life and cosmetic design change, I for one will probably pass on that. I think the current 3DS is designed well enough that I will be happy with it in its current form, with or without that add-on, for a long time. What really spoiled me in the last handheld generation, what will really make me give Nintendo money that I really can't afford, would be a 3DS XL. Now that gets me excited. When I went from my Lite to my XL, it was just amazing.