Gas: Consider multi-line surveys (e.g. Bergin et al. 1997, above) or multi-region single-line surveys, or multi-line, multi-region surveys)
To do much more:
Large-format mm/sub-mm detector arrays for spectroscopy on single-dishes (e.g. FCRAO's current SEQUOIA + future array for LMT; HHT/12-m/JCMT/CSO could all use one--CfA could build one?)
Interferometer surveys (merged BIMA/OVRO plus SMA could do nearest regions; ALMA & SKA will be best 10-30 year time horizon)
Dedicated telescopes (e.g. 12-m or post-LMT FCRAO could be dedicated to this, like CfA mini is now)
Better sites (consider Atacama 15-m collaboration--with spectral-line capablity, this would be better than FCRAO or 12-m, but time might be too limited for survey)
In general: Explore multi-institution collaboration to achieve large amount of time required for surveys (e.g. SMA-BIMA/OVRO collaborative projects)