Interesting question! I'm surprised it isn't asked more often...
I agree with RussianSensation, and I'm a nut when it comes to lapping. For instance, I lapped a Scythe Mine 3, roughed up again, then lapped it a second time, just to see what the difference would be.
Indeed, the Tuniq Tower 120 has a rough finish, however, this is such a brutal cooler that it really doesn't matter if it's shiny or not, nor which thermal compound you use!
I know this doesn't make any sense, but that's the way it is - they ARE flat (which is all that matters, in this case) - take it from someone that owns two Tuniq Tower 120s.
Having said that, I wouldn't worry about it, unless you're a tweak! It won't make any difference, but if it makes you *feel* better, go ahead and lap...