The idea of using i2c for inter-launchpad communication is a good one. With the use of RF parts like the ez430-RF2500T, a low-cost wireless sensor network can be created easily that matches the current best-runner (IMHO) in Arduino space: JeeNode, but at a lower cost. The MCU, MSP430F2274, in the RF2500T is decent: 32K flash, 1K RAM.
Instead of stacking "shields" (or "booster packs", etc.) on top of each other like in Arduino, you can divide and conquer. Split the large problem into smaller units.
One of the projects I'm working on, an accelerometer-connected 16x16 RGB LED matrix "c