Yes, there will be a Space Invaders Extreme 2. Those early retail listings weren't lying, with importer Nation Console Support adding new information on what the sequel will bring. It's bringing bingo.
According to NCS's write up of the Nintendo DS-bound sequel, the game's bingo mode works like so: "Taito throws in the classic game of Bingo where a grid is lit up during the course of a stage as invaders are shot. To win at Bingo, key spots on the grid must light up horizontally, vertically, or diagonally." Should be a hit at your local senior center!
Also coming to Space Invaders Extreme 2 is at least one new multiplayer mode, described mysteriously as having "new strategic considerations." Consider whether that's enough to sway you to buy the Japanese release, which ships March 26.
Space Invaders Extreme 2 [NCSX]