I would definitely wax it makes it easier to clean in the future by filling in all the microscopic peaks and valleys that dirt likes to grab on to. While your car will stay cleaner longer, you will notice that it still gets dirty when waxed. All it takes is a nice easy soap down and rinse to get the dirt off. How often you want to apply the wax is entirely up to you. Personally I do it about 2-3 times a year, 1 right before summer, 2 right before it starts to snow (helps keep salt spray and sand dust off the car) and sometimes an extra in the middle of summer (gotta let it shine baby!!!). Works out well for me, and I don't burn through wax that way!
And a $$ saving tip that car wash makers won't tell you, use dawn dish soap to wash you car, has the dirt and grime fighters in it, and it helps your car retain a sheen (it also it mild, won't harm your paint) it also cuts through disk brake dust really well...
And I never thought of WD40 for wax on the trim, but makes sense... Props LAMINI!!