A Multi-touch monitor is nice... but it's not a complete replacement for mouse/keyboard/control-surface.
Over time, I think multi-touch will diminish the need (desire) to invest in a control-surface.
Touch is relatively new... and will certainly be further refined/enhanced.
IMO, The problem with control surfaces is the lack of a clearly defined spec (like MIDI).
Mackie Control is the closest thing to that... but there are deviations within that protocol.
ie: NI's Machine in Mackie Control Mode when used with Sonar.
Sonar waits for a "handshake" (I believe a SysEx message from the MCU) that never happens... which leaves you in limbo.
At this point in time, unless you absolutely must have faders under fingers, I'd hold off buying a control surface.