The more you play the better feel you have for your level. I view the ratings as "broad bands." Some 4.0s are really good and should be able to beat low end 4.5s at times, while other 4.0s are still competitive with high end 3.5s. Just pick a number that makes you competitive in the league you are in.
For me, I was rated back when you had to go to a clinic--you couldn't self rate like you can today. I wanted a 4.0 rating, but got a 4.5 and, consequently, couldn't play in the league I wanted and had to go into a 5.0+ league. It just wasn't as much fun.
I once met a guy who said he "played" but didn't have a rating. I took this to mean he was probably a 3.5 or 4.0. Turns out, he won the state high school championship (10 years earlier) and had beaten McEnroe as a junior. He didn't have a rating because he was too good to have a rating. Similarly, my father (thirty years ago) once was hitting alone and this fat guy with loafers asked if he could hit with him. This guy proceeded to beat my dad 6-0, 6-0 in street shoes using a borrowed racket. Turns out he was captain of his team at Stanford and had "gained a few pounds." You never know what you are running into. My point is that despite its flaws, the ranking system at least gives a reference point.
Isn't enough to see that a garden is beautiful without having to believe there are fairies living at the bottom of it, too?