I just acquired a Sako 75 SS in 300 WM. Other than loads and trigger (the trigger is very good) what accuracy improvements (tweaking, not major changes) can be made to the base gun?

Have you shot it? Most probably you will find that this fine rifle will not be needing any improvements.

I had the barrel replaced in my Sako, but that was just for weight reasons.

Good luck and enjoy one of the best out-of-the-box rifles!

I shot the gun twice this weekend following the shoot/clean break in method. I would like this gun to be my primary hunting gun and would like to get it to its full potential.

Not much else needs to be done to a Sako to get it to shoot. But...
My gunsmith usually does a couple of extra tweaks to get the most of a Sako 75. Skim beds and recrowns. The bolt is smoothed up even more and feels like it's on ballbearings. Not a hitch is present even when opening and closing the bolt. Trigger also gets a little minor tune up. Not a lot of difference from start to finish, but it is noticible.
The groups are usually down in the 1/2 inch range when he gets done. For a couple of hundred extra (at most) I think it's worth it. A Sako usually doesn't need tweaking to be a good shooter but most Sako's become great shooters when he gets done. His son uses a Sako 6PPC to shoot in the stock rifle class and usually wins with it.

When hunting I like to use a stockpack on my model 75's like this one:

http://www.eagleindustries.com/MainProd.asp?CatID=23&SubCatID=69

It helps me get a better cheek weld and I store a pull through/obstruction remover and a ballistic data card in it. Weighs less than you might think.
On my Finnlites I filled the butt with "Great Stuff" expanding foam to get rid of the hollow sound but didn't find it neccessary on the std model 75's.
I've had 3 30 cal Sako 75's and for whatever reason all of them have shot Failsafes quite well. I think the bores may be a little on the large size. A 180gr Failsafe might be a good idea to try in your 300 Win Mag.
In 300 Win Mag, I've had great luck with 75-77grs (max load) of RL-22 and 180gr Bullets. You might give this combo a try. Me and my freinds have tried this combo in close to a dozen 300 Win Mags with excellent results. Some shot best with Partitions and some loved Accubonds.
Other than that enjoy a great rifle, congratulations................DJ

DJ,

I sent you a PM.