I don't think there's a point to it really. I'm coming up on a year with the same application, and my temperatures are pretty much the same as they've been all year (+ or - ambient fluxes...sitting at 102F right now, with 86 case temp, nice cool spring night outside)
I did notice things creeping up a little bit, but my apartment is extremely dusty, and the case was very mucked up. So I took 45 minutes and gave it a good once over...cleaned off my fans, wiped it down a bit...blew on the board a few times to get the most prominent dust off and closed her back up...back to about normal!
Once i get a some canned air I'll go in and puff out the heatsink and give the mobo another dusting, but I don't expect much of a difference.