What you say is pretty much correct Joe - when in VNAV Path the pitch mode on the FMA is maintaining a desired Path not Pitch. Iznogood isn't technically correct regarding how VNav Speed exactly like LVL CHG.
The difference between LVL CHG and VNAV SPD is that imagine you were descending from A to C via B, and B had an AT or ABOVE altitude set in the FMC. VNAV SPD would ensure you crossed at or above, and would level you off to ensure that restriction at B was met if necessary, regardless of what altitude was set in the MCP window. (And unless I'm mistaken, it'd actually flick over to VNAV path if it needed to level off to comply with the restriction at B, even with speed window open. It'd flick back to VNav SPD once the restriction at B had been complied with).
LVL CHG wouldn't. It would simply be an idle descent from A to C at the Speed set in the MCP window, ignoring any restrictions set at B.