It's a good idea. After all your bolting on a real thin cover that distorts easily. The torque spec is 20 ft. lbs. I'd tighten them to 10 first then go back around tightening them to 20. Before you install it make sure you lay the cover on a perfectly flat table or bench and verify the holes aren't distorted. If so use a small hammer to tap them back out flat. You want that cover as flat as possible or it may leak.
BTW: the brake T is not a valve, just a distribution block that connects the single line coming from the M/cyl to both wheels. Mine looked just as bad as yours when I bought my car. 5 minutes with a can of carb cleaner and a quick polish with a wire wheel and it looked like new. Replace the hose and lines of course. They can break down from the inside and you never know it's a problem until they blow and you have no brakes.