If that's what you have and it works for you, great. I prefer to use a power beyond configuration, rather than allow for pressure to build up on the return side. Your valve appears to be capable of power beyond, it would be a matter of locating the right sleeve and adding another hose.
There's nothing wrong with the two port adapter, but they usually have tapered pipe thread ports, which I don't care for. Also I need to find a separate sump return port somewhere on the tractor. Sometimes that's easy, sometimes not.
As for the actual problem. There really is no true filter on the three cylinder 4000. There is a suction screen on the hydraulic pump inlet. It's not exactly easy to get to, but if partially plugged it can certainly affect pump performance. If you're having hydraulic problems that affect both the loader and the three point, then I would be looking in that area before condemning the loader valve.