On the CA (collection agency), paying it to $0 will not improve your score unless you get them to accept a Pay for Delete (PFD). FICO doesn't care if you owe $0 or $10,000, it is still read as a collection.
Paying down your CCs will absolutely help! About 30% or 35% (someone correct me) of your FICO score is utilization. Ideally you want each individual balance to report less than 10% of your utilization. You'd also want about 1/2 of your CCs to report at $0. Roughly and unofficially, you'd get 10 FICO points per every 10% of overall utilization you bring down. So, if your util is at 60% and you pay to 0%, your increase is roughly 60 points across each CRA. YMMV.
