I wouldn't worry about wearing out a 4513TSW. I've fired many thousands of rounds through that model without a problem. The wear on the aluminum frame shoulders concerned me greatly at first. But it appears to wear to a point and stop. The 4513's are fine carry 45's. One of my personal favorites. I've bet my life on them and have no complaints.
As to the HK USP 45 compact's, they are fine pistols. They are available in DA/SA as well as with the LEM DAO trigger. The LEM variant I tried was not for me. I own the traditional double action variant.
While the 4516 is a fine pistol and I am an ardent fan, the USP 45 compact is superior to the S&W 45 compacts in a couple of areas. Weight and capacity being the primary USP compact advantages. The USP 45 compact carries 9 rounds vice the 4516's 8 rounds. Fully loaded the USP 45 compact is still lighter than the 4516. I have also found that the USP 45 compact is slightly more accurate than my standard production S&W 45 compacts and almost as accurate as my Performance Center Shorty 45. Almost.
The only category the USP 45 compact fails in, for me, is its double action trigger pull. The USP 45 compacts DA trigger is almost as bad as the M&P's trigger. Almost

. Slightly gritty, heavy and stacks before the break. SA is as good as any 1911 I've shot and on par with the S&W 3rd gen 45's. Very crisp. I guess thats why so many users carry their USP cocked and locked. All of the traditional double action USP variants are capable of cocked and locked carry. The USP was designed with some 1911 features in mind. I have found that the USP 45 compacts DA trigger does smooth out as you "wear it in". Not enougth, for me, to date.
I am currently going to see an HK armorer in Asheville NC. He claims he can improve the DA trigger pull on my HK USP 45 compact by smoothing a few parts and changing out a hammer spring. We'll see.
As far as the HK USP prices are concerned, you get what you pay for - in the case of HK products anyway. I've owned HK USP handguns since 1995. I currently own 4 and have owned several others over the years that I've sold for various reasons - none of those reasons being the HK handgun itself.

I've yet to pay more than $650 for an HK product. Deals are out there if you look around a little.
People who pay full retail are usually in a hurry or don't know what a gun is worth, in my experience. Personally, I will gladly pay $700 for an HK pistol I want. I know it will be accurate and reliable right out of the box, with no need to rebuild a brand new gun using Apex parts or aftermarket barrels, just to make it useable.
Police trade ins are bargains. Some light holster wear - thats it. The guns shoot like brand new. Last June I picked up an HK USP 45 compact with original case, three mags and Trijicon night sights. $479 OTD at Lawmans Safety supply in Raleigh NC. Last December I picked up a USP full size 45 with case, three mags and Trijicon night sights for $650 OTD at Striechers police supply in Greensboro NC.
If you want, call Lawmens in Raliegh. They had around 20 USP 45 compacts left last time I was there and they ship out of state.
While I am a fan and proponent of the S&W 3rd gen 45's, I've got alot of time behind HK products and am a proponent of them as well. Other than the Walther PPQ, the HK's are the only polymer guns I own or want to own. Quality build, tack driving accuracy, bet your life reliability and they look good doing all that.
No need to mention HK's customer service either. In seventeen years I've never needed them. Neither has anyone else I know who owns them. Can't say that about other manufacturers.
Good luck with your decision! Hope this helps! Regards 18DAI