Ever notice that guitar tracks sound brighter and thinner than in the old days? Listen to Robin Trower or Jimmy Page tracks and see how round and mellow they are. Albert Collins used a 100 foot lead cord in order to walk through the audience and this gave him a unique sound. Hendrix would string Marshalls together like Christmas tree lights using cheap, lossy, coiled cords.
In the struggle to be heard above the cymbals on overcrowded stages and fighting the gradual loss of hearing from night after night of loud music and people shouting in your ear in bars, guitarists seek to counter the muddiness by increasing the top end. Modern pedals mostly all employ active switching these days and this acts like a buffer in order to prevent loss of high end. For years I bypassed the tone controls on my Strats to get more bite. I used buffers before my Univibe, Ecoplex, Wah pedals, Boss Chorus Ensemble.... pretty much everything. I even had buffers in my guitars.
Now I'm going the other route. I like the sound of the guitar plugged into these old effects without any buffering. I find that the Univibe is rounder and richer, the wah less shrill, and the Echoplex just fine. I reconnected the tone controls back into my Strats and, hey, the sound is much richer. The trick to the whole thing is to use a buffer when the pedals are bypassed so as not to lose too much high end from all the extra wiring that is necessary to hook-up the pedals together as well as to prevent the loading effect that these old pedals have on your sound..... not always an easy thing to accomplish.