I've narrowed my first HK purchase down to the USP 9 full size and the USP 9 SD.

The only real differences that I can determine are the match sites and the threaded barrel, and of course, the $150 price difference.

Since I don't really plan on ever getting a silencer (I'd rather spend that dough on a new scope for my AR and reloading equipment), is the match sites really worth the price difference? How easy is it to upgrade the sites in the future if I want?

Thanks in advance for any opinions.

I've owned a USP40, and USP45.  Both are great guns!  I much prefer combat style sights, and infact shoot better with basic combat s/sights. Just my $0.02
Good luck.  

ps, HK makes great stuff.            

Personally, I'd skip the threaded barrel, IMO. As you say you won't be using a silencer so why bother?

Yes, sights are easily changed when you're ready.