Engine Re-Build on a '99?

I've the '99 V6, running decent (other than rough idling, a slow oil leak, spark knock, and the fuel economy gone to Hell). I originally had intentions for it to be my project car, then thought of trading it in for a truck - but I've decided to simply keep it, and put it back in near-new running order to give to my wife next year.

So, come tax refund time, I intend to put several hundred dollars into this pony to extend the life and performance of the engine, with the help of a mechanic friend of mine. At the very least, I intend to replace all filters, plugs/wires, bolts, gaskets, and clean the heads/cylinder chambers. What else can I do? Any articles/experience on this? Any specific parts I need to replace (and the best sources for those parts, if possible)? Any such 'rebuild kit' for this kind of job?

I'm trying to 'blueprint' the job ahead of time, and any advice is greatly appreciated.

Thanks!

The engine has about 129,500 miles on it.

I'm also considering, since I'll be on limited time to make the re-build, to try and purchase a re-machined short block assembly, and use my existing headers, heads, intake, etc.

I read on another post where someone suggested to 'seafoam' the car - how exactly is that done? I don't want to do a re-build unless necessary, but I'm beginning to wonder if it's necessary.

Any places online that offer decently-priced (re-built) short block assemblies?