1. Joint bar-IFO observations
The activity of Working Group 2 of the Network GWA is on "Joint operation of detectors and network data analysis" and they are committed to make recommendations to our European community on the opportunities of joint observations with the operating detectors in the next 5 years. The activity is starting and suggestions on specific topics or requests are welcome and can be forwarded to any member of the WG2.
(current co-chairs: B. Sathyaprakash, G.A.Prodi).

2. Why do we need to exploit the greatest number of available detectors ?
the confidence of detection is mainly set by the rate of false alarms. The behavior of the false alarm rate versus signal amplitude is crucially dependent on the number of the detectors which effectively participate to the observations. As IGEC showed in and LIGO is showing, adding one effective detector to the joint observations makes a difference of one to a few orders of magnitude in the measured rate of false alarms versus signal strength. From experience, the false alarms get reasonably low even at low signal amplitudes with at least three detectors with the same directional sensitivity.
the efficiency of the sky coverage requires to add detectors with different directional sensitivities, with a strong overposition of antenna patterns as required by the previous point. Bar detectors are more effective than interferometers in covering the sky (on average by sqrt(2)) and can be re-oriented (see ALLEGRO-LIGO collaboration) to optimize the sky coverage of the network of detectors. Spherical detectors are even better.
the duty cycle for long term observations. From experience, detectors are not generally 100% of the time in effective operation.

3. Which detectors are effective for a specific signal ?
of course it depends on the detector noise (Shh) and the signal characteristics. Narrower bandwidth detectors will be sensitive to a narrower class of signals. IFOs show significant advantages over operating resonant detectors, no doubts.
the actual Signal to Noise Ratio at which a specific signal is detected depends also on the kind of filter implemented, in particular on how much the filter can be matched to the signal. In general the efficiency of the data analysis for any specific signal template has to be estimated by Monte Carlo on real data. This is currently a matter of study. The situation is even more puzzling for a search for signals with unknown template.
For instance:
for the sine-gaussian signals used by LIGO in the S3 analysis as templates for the burst signal search, a detector with the bandwidth of 100 Hz (AURIGA) is almost as efficient as a broader band detector, for central frequencies within the 100 Hz band.