it may be overkill or underkill but if the statistics that are needed are contained in the tcp/udp header (srcip, dstip, srcport, dstport, length, flags, ...) say for counting the number of connections/packets/data/protocol between hosts then use flow-tools and Cflow.

parse the firewall logs with Perl using the Cflow module to convert to netflow format, it holds data you find in the IP headers and some more. then use the flow-tools to process them. there is a learning curve, but it's worth it.

the simplest Perl version of say counting the number of packets and bytes transfered between a given pair of hosts over enough time/data so that the script takes 1 minute to run. well, the equivalent flow-tools command will do the same in 2 seconds. it does nice text-based reports, scan detection, powerfull filtering and there's excellent support on the mailing list.

if you're counting based on the data in the packet like specific intrusion attempt types then flow-tools won't do much good. if you have lots of header type data flow-tools rocks.