I'm not going to be gaming on this machine, strictly a photo editing box, but there will be a lot of intensive batch processing which typically take anywhere from 30-60 minutes depending on the action running.
It will help. And 3.2 is an easy speed for the processor you plan on getting. I recommend you test it for yourself when you get all the parts. Just bench her at stock with your own tests, the ones that matter for you, and get a base line view of her performance, then get to over clocking and you can tell us the difference in time overclocking saves!
And since it's free beyond ordering the parts, why not, if it helps?
As far as CPU life goes, I doubt 3.2 would do anything to it, really. Just watch the temps and all that jazz, and you'll be good to go!
I have the same board here, though not with a 45 NM chip, so i can help ya when you need it!
As jsc suggests, it all depends on whether your batch processing is CPU limited or hard-drive limited. If the time is mostly spent calculating (for example filters/blends/rendering), then OCing the CPU should help pretty directly (i.e. I'd expect close to 20% task speed increase from a 20% overclock). If the time is mostly spent loading/saving large image files, then speeding up the disks should be your priority. RAID 0 will essentially double the loading/saving speed, but doubles the risk of data loss due to drive failure. I'd go with a RAID 0+1 setup (4 drives, giving double throughput and full data duplication, but only the storage space equivalent of 2 drives).