It's a matter of preference and personal taste.
To me, I like the look. It really is aestetically pleasing, however...
It IS
very very functional.
My moms Highlander does not have it, and the back window and tailgate is
always filthy. Vacuum draft is created by the design of the H/L. I drove it for three weeks last winter.
Spoiler becomes an effective
sun shade as well.
The functional design of the Highlander spoiler was perfect, and it will not affect the downforce. The inner scoop that directs air down the glass is not dramatic at all, but just right to deflect a strong rush of air downward even at 30MPH in my opinion. At 30 the water sheds completely at that speed. I never need to use the rear wiper except maybe to give a quick washer sweep when H/L RR window gets dirty with mud etc.
Also, I feel my H/L Limited with spoiler as standard equipment would look incorrect if I chose to take it off. But, I'm a purist.
Take it off. and tape the holes for a trial run for several months and see if yu really want to do without it. I think it's foolish.
That's for yu to decide in any event yu choose.
It tends to be a sought after item for many Base Highlander owners. And doesn't come cheap. $200-$300 depends if color keyed or not and must be installed correctly. The retrofit doesn't take 5 minutes either. So installation might be another $75 or so for an hours labor time.
My two cents
LT